Move to IP telephony provider-independently, with zero downtime
ISDN Migration to VoIP
ISDN migration in Austria: A1 switches ISDN off by mid-2026. Anexum guides the move to VoIP and SIP trunking - provider-independent, with number porting and zero downtime.
Plan your ISDN migrationWhat is ISDN Migration to VoIP?
ISDN migration is the move from classic ISDN telephony to IP-based voice communication (VoIP). In Austria, A1 switches off ISDN multi-connections at the end of 2025 and basic connections by mid-2026; in Germany ISDN is already off. 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.
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.
When is ISDN switched off in Austria?
A1 switches off ISDN multi-connections at the end of 2025 and ISDN basic connections by mid-2026. In Germany, ISDN was switched off back in 2018-2020. New connections have long been unavailable, so the migration should be planned soon.
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.
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.