Re: EMAIL option in GPRS
As you clarified in your post SMTP would be actually the protocol to send Email while POP3 is for reception. There are basically two options, I think. To reuse existing TCPIP and SMTP/POP3 code from other projects or to write it from the scratch using respective RFCs. Knowledge of the RFCs is helpful to better understand existing code anyway.
I also don't know, if TCP communication has to be set up from the bottom through PPP with SIMCOM 300S or if higher level interface is provided. If complete PPP and IP stack has to be designed, I would try to get suitable code from an existing source. Or did you already implement basic TCP service in your project and only need EMail add-on?
Regarding Email through SMS, I included this option in a project with automatic SMS alarm. But the project initially used a GSM modem without GPRS capability, so there was no other option anyway. German t-mobile is charging standard SMS rates for SMS to Email now. Of course, you have a length limitation of 160 chars. For s high number of messages, GPRS would be more cost effective.