When choosing the modem be sure it is one that can have a SIM tool kit(STK) app written for it unlike the current modem on the N900. Between banking, electronic crypto legal signature, and the NFC "credit card" function it would be a big loss not to have the STK functionality again. OTOH it would also be great being able to 100% block the STK apps as desired like we spoke of with the GPS antenna since some of them might be considered problematic by the user.
I was never clear why the N900 couldn't have a STK app but I assume it is the closed modem driver.
If it would help I can dig out my GTA02 and see if it has STK.
https://en.wikipedia.org/wiki/SIM_Application_Toolkit
SIM phonebook access, import, export would also be nice.