Iphone

I'm pursuing my Master in Communications and trying to decide on my thesis. I´m trying to establish a seamless roaming between GRPS and WLAN in a laptop (of course I would have a Wi-Fi card and a GPRS PCMCIA card). I mean, the laptop could access internet/email/... from both networks without loosing the session when roaming bw them.

I have read several docs in IEEE and 3GPP and think the best solution is to use a tight coupling approach, the WLAN acts as another RAN on the GPRS network. To achieve this, a IEEE document recommends to add a protocol called WAF (Wireless Adaptation Function) in the middle of the LLC and RLC/MAC layers. The WAF signals the activation of WLAN interface when entering a WLAN area. It also signals the change of RA to GMM, supports the paging procedure. etc.

I have read all the questions/answers posted here. Very helpful.

Some my questions are:
1. I haven't found a PCMCIA card for GPRS, anyone knows about one comercially available ?
2. Since I need to add the WAF layer, I could not use a current phone (because I cannot modify the protocol stack) so I need a internal GPRS modem so I can modify the stack of protocols in the laptop. Any recommendation about the best environment to do this I mean to use Linux (this way I only have to introduce my code for the WAF layer) or use some Active X alredy developed?
3. How does the IP assigment work in GPRS? Does my IP change when moving to another Routing Area or do I have the same IP all the time moving to other cells, Routing Areas?
4. This is becoming a big project, do you know any company, university or people working on this?

Iphone

1/ Nokia D211 or Sony Ericsson GC75

2/ Forget it, see the previous comment, if you're going to do this it will have to be at the application layer, regardless of approvals no-one is going to give you the source code to thier module. Reading your question a bit closer you imply that you can't use a regular phone to do this for exactly this reason, Unfortunatly a PC-Card phone or external modem works exactly the same way as any other phone, IE all the smarts are in the card none of the GPRS stack is implemented in the PC.

3/ As per the other poster but in Australia you don't get dropped for inactivity that quickly.

4/
If you've not yet done so have a look at Mobile IP, you might like to start here:-

IEEE Internet Computing

This set of protocols does exactly what you're looking to do.

I've never heard of it being implemented on a GPRS network though (but it could be).
I have personally implememented it for a CDMA 1x terminal device.