Device-to-device data call

Hello!

Sorry if this is a silly question, I'm definitely a noob, but I'm in need  
of some information before starting development. I don't have any real  
devices at this time to try it on, and I can't test it using the emulator.

I see that I can establish a data link between two devices using  
CTelephony::EstablishDataCall method. The link is then represented by the  
RComm instance. I understand that GPRS is a packed based service -- so why  
is it represented by a serial-like interface. Ok, so maybe the underlying  
protocol is packet-based and is hidden from us, but why with a serial-like  
interface?

Does the stablished connection provide error correction? Is there a way to  
provide packet framing on it other than me writing a SLIP-like protocol on  
top? Can I start PPP after the connection has been made?

I would be very grateful for any kind of information.
Thank you.

With kind regards,