[Discuss-gnuradio] USDR-based GSM/UMTS handset?

(Re-sendung this after subscribing. Apologies if it ends up being sent twice. By the way, is there a way to only receive answers to one's own messages?)

Hello,

I'm afraid that I am very naive in radio matters (I hope to gradually
change that - reading recommendations welcome!), though I have
reasonable understanding of computer hardware driving from the
computer side, and am working on learning electonics (that is, working
through Scherz and Monk's Practical Electronics).  I was wondering
whether it is possible, using existing free software and a USDR
(presumably in combination with a SIM card interface, and an RPi or
whatever) to recreate a GSM/UMTS handset.  And if not, how close one
can currently get.

Thanks!
Regards
Michael