Hashcode: US GSM networks work perfectly on the XT883 radio using the build.prop I made based on your 10-18 CM10 Kexec (and works on latest as well.) Info and uploaded here;
http://xdaforums.com/showpost.php?p=33102553&postcount=422 I get HSPA 14.4Mbps (actual speeds around 5.5 on att in my area) and it shows an H instead of 3g
Wish mavrom did that.
For others needing info, read the thread in dev section for unlocking for att/tmobile, I post my findings there. Including (awhile back) of getting somewhat dual mode on us vze/gsm without radio swap. I was able to receive sms, calls, and 3g data on vzw with xt883 radio, couldn't call out or send sms (could use google voice for sms and grooveip for calls over data though). Then swap to gsm mode for my sim.
Back on subject, built in tether works on xt883 gsm fine, mms, etc. Only issues are known issues, all radio aspects work.