Welcome to the wonderful world of CODEC (Code/Decode) data packets. RTP packets get used in lots of ways, especially with SIP circuits.It could be you're encountering a mismatch between the type of packet you're sending with the type of packet the cell provider will accept. Cell providers have probably reasoned that there would not really be a need for someone to remotely route a call through a cell phone, so accepting/reading DTMF tones was not considered useful.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.