SIM900 and TCPNet not working

I try to use TCPnet to dial GPRS using sim900 GSM modem and I try to many difenrent things but TCPnet ppp just simply don’t work for sim900 any help?!
As far as I know problem is sim900 return echo and accept commands with \r\n and TCPNET send commands using \r and it return any reply using ECHO\r\r\nREPLY\r\n and yet another thing is there is no way to set APN using TCPNet any suggest to do that