The reason I asked the question about usage outside of the US was because of the CDMA/GSM issue. I have ATT's 3g system and am very happy with it, but I think EVDO coverage is still a little more extensive.

I tether on an HTC Tytn and it is very good. On my wife's TyTN II, the connection speed matches my Sierra 881 aircard (which usually remains in my desk drawer). On HSDPA and HSPA you can take calls and surf simultaneously. On the slower EDGE area, you can only do one or other. I have a friend with Sprint Blackberry with tethering and is thrilled with it.

TMobile's internet is the cheapest, but they are only EDGE. There will be limited 3g on TMobile in a couple of months, but I'm mostly posting this because someone will call me out if I don't. NYC is live; other major metro areas will go live in the fall.