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Move to IP telephony provider-independently, with zero downtime

ISDN Migration to VoIP

ISDN migration in Austria: A1 switched ISDN off on 30 June 2026. Anexum guides the move to VoIP and SIP trunking - provider-independent, with number porting and zero downtime.

Plan your ISDN migration

What is ISDN Migration to VoIP?

ISDN migration is the move from classic ISDN telephony to IP-based voice communication (VoIP). In Austria, ISDN in the A1 network is switched off: basic connections on 31 December 2025, multi-connections on 30 June 2026; in Germany ISDN has been off for years. Anyone still on a legacy or transitional setup should move now. Anexum plans and guides the move provider-independently: an inventory, a choice between SIP trunking and a cloud phone system, number porting, and migration with zero downtime. Existing phone systems are integrated through a SIP gateway where that makes sense.

How it runs

A migration nobody should notice in daily work

The migration is structured by numbers, sites, and criticality, with a pilot, tests, and a rollback option before every cutover.

  1. 01

    Baseline

    Record numbers, phone systems, contracts, and dependencies.

  2. 02

    Target

    Choose SIP trunk or cloud PBX, define routing and emergency behavior.

  3. 03

    Pilot

    One user group validates features and the support path in live use.

  4. 04

    Port & cutover

    Port the numbers and cut over, with tests and a rollback option.

  5. 05

    Operate

    Continuously monitor and optimize quality and reachability.

Service scope

  • Inventory of connections, phone system, and numbers
  • Move to SIP trunking or a cloud phone system
  • Number porting with no loss of numbers
  • Integration of existing PBXs via SIP gateway
  • Provider-independent selection, no lock-in
  • Migration with zero downtime
  • Optional failover over mobile

No provider lock-in

Instead of an adapter with a long contract, Anexum picks the solution to fit your needs. You keep the freedom to change provider and technology later.

Zero downtime

The switch is planned and tested so that reachability and numbers stay available throughout.

One point of contact

Provider coordination, telephony, and internet access run through one team that knows your sites.

Common questions

When was ISDN switched off in Austria?
A1 switched off ISDN basic connections on 31 December 2025 and ISDN multi-connections, per its official announcement, on 30 June 2026. In Germany, ISDN has been gone since 2018-2020. Anyone still using a transitional setup or an adapter should complete the migration to a permanent VoIP solution now, before contract renewals or outages force the move.
Do I have to replace my phone system entirely?
Not necessarily. A SIP-capable system connects directly to a SIP trunk; an older system connects through a SIP gateway. Alternatively, a cloud phone system replaces your own hardware completely. Anexum assesses what is economical for your system and sites.
What does migrating from ISDN to VoIP cost?
Cost depends on the number of connections and extensions, the existing system, the chosen solution (SIP trunk or cloud phone system), and hardware. Anexum prepares a per-site quote rather than a flat price. No flat prices are stated on this page.
Can I keep my existing phone numbers?
Yes. Number porting is legally guaranteed in Austria (TKG 2021). Existing numbers are carried over to the new solution; porting is scheduled with the switchover in the migration plan.
SIP trunking or a cloud phone system - which is better?
SIP trunking suits cases where a working phone system stays and only the ISDN connection is replaced. A cloud phone system makes sense when you do not want to run your own hardware or need to connect sites and home offices flexibly. The decision depends on your existing setup, sites, and requirements. For a detailed comparison with costs, see the cloud phone system guide; for Microsoft environments, the guide on setting up Teams telephony.
How do I avoid provider lock-in during the migration?
By not tying the solution to a single provider. Anexum is carrier-independent and chooses the connection and telephony to fit your needs, instead of selling an adapter on a multi-year contract at fixed list prices. That keeps a later switch possible.
How does zero-downtime migration work?
The new connection is built and tested in parallel before the switchover. Number porting, system configuration, and failover are checked in advance. Only after a successful test does the switch happen, so reachability is preserved.

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Plan the move from ISDN to SIP

Plan your ISDN migration