I'm afraid my previously post wasn't clear enough.. my English sucks..
I have a OBi202 in US, caller(102) make the calls from a MicroSIP windows client to my OBI202 SP2(101) with a kamailio server which located in China.
What I want is I can call any US numbers directly from China side, right now I can only use the "sp1(18005551212)" to ring a fixed number only, and AA option 2 will do the bridge but needs an extra step.
Make a VPN service on the China server is possible but it's not an option, because China blocked all google services, same thing happens on the Hanhouts app.
I saw bpxes free account has a "Monthly Bandwidth Usage", I'll ask them if they has this limit between the extensions.
Anyway, thanks for the info, I appreciate.