First of all: I tried it with some Yealink, Snom and Panasonic phones, it works.
I have tried to setup 2 different FreePBX Installations. Each one has his own Public IP.
With a warm Spare Backup i sync the 2 Systems once a day.
I created a hostname for my pbx and made a A record with TTL 120 seconds.
So if the first PBX fails i just have to change the A Records IP Address to the second PBX and then i have to enable the SIP Trunk.
The phones change to the new Server after a few minutes.
Is this a good scenario idea or do i just have luck with the phones i use?
The idea sounds good for a manual Failover scenario.
My Providers offer api’s for this, so maybe i also can make i auto failover with some scripts.
In your case, if you have a warm spare, then simply add in your phones a secondary SIP Server (Your Warm Spare). Also most providers have a failover feature, so you can give them your secondary PBX IP for failover.
(Tip: we are using Sangoma Phones and added our warm spare’s address in the redundancy section in Endpoint Manager, i timed it once, it took a max of 10 seconds until all phones checked in to the warm spare.)
Wow, this sounds very nice. In our case the providers we work with do not offer failover trunks. The only way they have is to set a number for call forward if the trunk is not registred.