Ahmed, those phones are not technically designed to work with other PBXs, but you may be able to get it to work. Any information on provisioning will be located here:
The Adtran 706 does work with hosted SIP services. As with all standards, there is some flexibility in the standard that translates to configuration for one manufacturer not exactly matching every other. In my first attempts with the 706 to Fongo, I set up the Registration server as described in the Administrator Manual. The phone was great for incoming calls but was not able to dial out (fast busy response from phone).
The issue is that in some vendors, Proxyserver and Registrationserver are interchangeable. Not with Adtran. If I use ProxyServer, the phone does not register/authenticate with the hosted service. If I use Registrationserver, it connects but is not able to dial out. The answer is that I need both.
RegServer.0.Address.1 10.10.20.1 --- this can be IP as shown or FQDN
ProxyServer.0.Address.1 10.10.20.1 --- same as RegServer
The 706 supports server groups 0-5 while the 712 supports groups 0-11. This appears to allow individual configuration for each of the multiple lines. I can not see how to change the SIPUDPPort individually by server though. This is not a problem if all servers use the same port but in my case, the alternate server uses an alternate UDP port for SIP for ISPs that block port 5060.
Other configuration options will increase the robustness with alternates, secondaries, etc.
If you are using a hosted SIP service, you will have a username and password that need to be programmed.
Change the 0 for each of the lines being defined and then map the lines to the buttons.