i want to use a single sbc for all remote devices

[gkal]

is it possible to use vpn to connect to routers of ip phones and sbc, and everything works.

 

[Alphabetic]

Yes its possible to connect all your sites via VPN and set your routing up accordingly - good luck.

 

[NicholasP_3CX]

is it possible to use vpn to connect to routers of ip phones and sbc, and everything works.

If you have VPN connectivity between your sites and the PBX you will not need to have an SBC. The phones would then be considered as local to the PBX.