Any cheap GSM OEM module?

["Edu" <edugimeno@xxxxxxxxxxx>]

Hello!

I want to start a project that has been in my mind for some time, and I
need a GSM oem module to remotely send messages to my controller. I
only need it to decode DTMF, not real modem features, but this wouldn't
bother.
I need it to be very easy to integrate and cheap, because it is a
project for myself and I cannot waste too much, just in case it doesn't
work...

Thanks in advance!