Virtual PBX and Asterisk pbx

I already built a asterisk PBX,now i want to find a virtual pbx service that support trunk with my system.
i used trial of Onsip.com but thay can’t intergrated with my asterisk pbx.
Someone can tell me what service i can use.
Thanks all.

Maybe this one:
http://www.freepbx.org/freepbx-trunks