COMtrexx® Flex

Future-proof PBX appliance with optional legacy interface for up to 250 users

Flexible scalability through user-based licensing (up to 250 users)

Modern and transparent system

Optimised for the operation with Auerswald D-series desk phones

Mobile Work with COMfortel SoftPhone

Can be used variably with 12 analogue ports and second Ethernet interface

Your advantages in detail

COMtrexx Flex is the all-in-one VoIP solution for up to 250 users and a maximum of 48 simultaneous calls. Ten COMtrexx floating user licences are already included in the scope of delivery. The modular FXS gateway also offers the convenient and fast connection of up to 12 analogue end devices (e.g. fax machines and door terminals). In addition to the existing Gigabit Ethernet interface, a further GbE interface can be retrofitted.

The most important facts in brief:

  • Powerful "Ready-to-Run" VoIP exchange with 10 COMtrexx user licences
  • Modularly expandable
  • Flexible and cost-efficient scalability thanks to floating user licensing (up to 250 users)
  • Roaming user function for setting up mobile work environments
  • Optimised for operation with Auerswald D-Series desk phones
  • Fully automated registration of end devices using the latest generation of zero-touch provisioning
  • Integrated conference option with up to 10 conference rooms that can be used simultaneously
  • Comfort functions such as CTI, MWI and BLF with COMfortel D-Series
  • Centralised caller lists
  • Convenient and secure remote monitoring and backup via COMtrexx Control Centre

Mobile working is easily and securely supported by optional soft clients for computers, tablets and smartphones. The cost-effective COMfortel SoftPhone for voice and chat is available at the entry level. Those who need more extensive functions and more intensive integration into business processes will find the optimal UCC solution with PBX Call Assist.

Compatible products

Features & technical data

Everything you need to know about our products comes now. Scroll down for more information.

Comfort Features

  • Up to 250 users licensable
  • Up to 5 end devices or soft clients (e.g. COMfortel SoftPhone) can be used per user
  • Up to 48 parallel calls possible
  • Automatic control centre (maximum 10 configurable)
  • Presence status with the COMfortel D-Series
  • Barred/approved numbers, 10 each for coming and going, total maximum 200
  • Call of any second destination in parallel to the registered primary device
  • Call data management with 18,000 data records
  • Call pick-up (e.g. from the integrated voicemail or from mobile app COMfortel SoftPhone)
  • Broker and mediate
  • Pickup
  • Text before signalling (can be switched for groups and for the automatic switchboard)
  • Protection against attacks by setting blocking lists (blocked IP addresses) and activating blocking times
  • Situation-dependent call forwarding for offices, users and user groups
  • Urgent call (breaking through do not disturb for internal calls), follow me, parallel call, call waiting, open enquiries/parking calls), and much more.
  • Autoprovisioning for standard SIP phones1
  • Music on hold with switchable announcement text
  • Roaming user function
    • Enables individual users to log on and off at different telephones
    • Personal caller lists can be transferred to different workplaces
  • Centrally stored caller lists
    • User-specific caller lists are stored centrally in the system
    • Stored lists are available when a user logs on via the telephone
    • Access only possible via the user
  • Setting up groups
    • 64 call groups
    • up to 40 members per group
    • Fixed channels can be reserved for group calls
  • Logging in and logging out a user via a telephone by PIN dial-in
  • Registration of up to 500 terminals possible

SIP convenience features for standard SIP phones

  • SIP-BLF, Busy Lamp Field acc. to RFC 4235
  • SIP-MWI (Message Waiting Indication), monitoring of the central voicemail and fax boxes acc. to RFC 3842
  • Pickup pre-check2

Communication platforms

  • Up to 30 internal channels can be assigned simultaneously across all conference rooms
  • Up to 10 conference rooms with 10 internal participants each (audio)

Central address books

  • 2,000 contacts
  • Separate address books for departments and multi-company operation
  • Import of VCF and CSV files
  • Address book provisioning via LDAP

VoIP telephony

  • VoIP point-to-multipoint and point-to-point connection (SIP trunking)
  • Call forwarding on busy (CFB), no reply (CFNR), unconditional (CFU) at carrier trunk, configuration dependent
  • Call deflection
  • Transfer of customer-specific calling number information with outgoing calls (CLIP no screening)
  • High voice quality through optimised echo cancellation and wideband audio with G.722
  • Compatible to standard SIP telephones
  • SIP compliant with RFC 3261
  • Reservation of speech channels
  • Support of soft clients and COMfortel Softphone
  • VoIP-Codecs: G.711, G.722
  • Dynamic internal/external VoIP channels
  • Encryption of signalling/signalling (SIPS) and voice data (SRTP) for internal calls
  • Integration of external extensions (information on the location of the telephone is taken into account in an emergency call) and mobile clients

Voicemail and fax

  • Substitute function
  • Call acceptance and individual announcements depending on calling number, time and call type
  • Remote access of the voicemail boxes incl. voice guidance
  • Message and fax forwarding via e-mail
  • Up to 250 fax mailboxes, each with 500 messages per box
  • Up to 250 voicemail boxes, each with 500 messages per box
  • Maximum 32 channels can be used for voicemail and fax

UCC functions

  • Call journal
  • Instant messaging for a better sharing of information
  • Contact data for local users and out of external data bases
  • Platform independent (Windows, macOS, iOS, Android)
  • Presence management with automatic status detection
  • Alignment with MS Teams
  • Call setup and ending via the PC, incl. Outlook plug-in
  • Screen sharing for convinient cooperation
  • Softphone-functions for Windows, Android und iOS
  • Up to 250 users can be licensed

COMfortel SoftPhone

  • Softclient for the base functionality SIP telefony and messaging
  • Secure and simple PBX connection from anywhere via Auerswald cloud service
  • Softphone for Windows, iOS and Android

Software interfaces

  • Access address books via LDAP
  • Support of basic CTI function via action URLs3
  • COMtrexx REST-API

Unlockable options

  • User licence: Activates all functions of the Soft PBX and is required for linking users to a device. One licence must be activated for each active/registered user on the system4
  • PBX Call Assist
  • System activation (necessary for operation of the system)

Module connection options

  • Expansion by analogue ports with the COMpact 4FXS module (maximum 12 ports)
  • Extension by one Gigabit Ethernet port possible


  • The COMtrexx solutions can only be used in combination with floating user licences. You can obtain these and other licences from our authorised sales partners. Please note that additional services such as software maintenance and function extensions may cause additional costs.
1 Supported for telephone models D-600/D-400/D-210/D-200/D-110/D-100 and WS-500S/M IP-DECT systems. Also partially supported are telephone models from other manufacturers such as Yealink and Snom
2 Is only supported for the telephone models D-400/D-600 and D-210/D-200 in operation with an extension.
3 Is supported for the telephone models D-600/D-400/D-210/D-200/D-110/D-100 from Auerswald
4 The licence can be used by several users ("floating"), provided that the total number of active users corresponds to the total number of licences in the system.

Trunk lines 1



VoIP channels (SIP acc. RFC 3261), point-to-multipoint/point-to-point connection (SIP trunking)

0 - 96 96

VoIP codecs

G.711, G.722

User connection 1



VoIP subscribers

0 - 250 250

VoIP channels (SIP acc. RFC 3261)

0 - 96 96

VoIP codecs internal

G.711, G.722

Voicemail and fax system



Voicemail channels

8 8

Fax channels

8 8

Voicemail boxes / fax boxes

250 250

Fax standard

T.30/T.38 acc. to ITU-T

Additional connections 1



Ethernet ports 10/100/1000 Base-T (10/100/1000 MBit/s, twisted pair)

1 2

Analogue audio output for announcements (e.g. a/b Audiobox)

4 4

Module slots


Technical data



Operating voltage

230 V ±10 %, 50 Hz

Power consumption

5 W min. | 65 W max.


plastic, metal angles for 19" rack mounting

Dimensions (w x h x d)

325 mm x 88 mm x 240 mm

Weight (w/o modules)

approx. 1,700 g



Supported operating systems

Windows 7/8/10/11, macOS, Linux

  • 1 Possibly depending on the configuration of the telephone system
  • 2 All VoIP channels are freely configurable between internal, external and dynamic

Delivery Scope

  • Base unit
  • Voucher for 10 COMtrexx floating user licences
  • Operating manual


COMpact 4FXS Module

Expansion module for COMpact systems as well asl COMtrexx Business with four additional analogue extensions.

COMtrexx Flex GbE-NET-Module

Extension for COMtrexx Flex with a second Ethernet interface


COMfortel® SoftPhone

Softphone and messaging solution with mobile and secure connection to COMtrexx and COMpact ICT systems

PBX Call Assist 5

Unified communications solution with CTI, cross-media presence management and individual/group chat


COMfortel® WS-500S

The single-cell IP DECT system that can handle so much more when needed

COMfortel® WS-500M

One device, all scenarios: the WS-500M DECT multi-cell system ensures seamless mobile communication

COMfortel® D-600

High-level design – COMfortel D-600, the premium SIP device

COMfortel® D-400

Office or home office – the COMfortel D-400 SIP phone is the professional choice

COMfortel® D-210

Professional SIP-Phone  –  amazing range of premium functions despite almost entry-level price

COMfortel® D-110

Entry level terminal with professional feature set that quickly proves its worth in demanding everyday use

COMfortel® M-730

The tough one: designed for challenging working environments

COMfortel® M-720

The elegant one: compact, well-designed, and powerful

COMfortel® M-710

The versatile one: full featured at an unbeatable price. The ideal entry.


Top Sellers

Sales Configurator (SC)

- the easy way to the right system

Customer requirements for communication solutions are constantly increasing and with them the complexity and scalability of ITC systems. Project planning therefore takes up more and more time. Here, the free Sales Configurator offers a simple and fast solution. It gives you the opportunity to efficiently plan communication solutions and create project planning proposals.

Sales Configurator (SC)