Configure Cisco router for Ip phones access remotelly

Hello, Im configuring some ip phones that must register remotelly via SIP to a asterisk PBX box. remote phones can log in, but when a call is made none can heard and then phonecall hungup. I need someone that configure in a short period of time my router (because i think is problem of that). i can connect thru VPN to the remote server, that way i can call. but internet navigation get loss. i pay instantly for that $30 usd