Well, I have been in California for almost a week. I was at a mall in Burbank, hanging around, waiting for my wife to return from a store that interested her, when I started talking to some guys at a T-Mobile stand. It turns out that a lot of the goodies we take for granted are still on the future horizon here. They had heard of, but didn't offer any of the Nokia N series phones. HSDPA, which we don't have but will soon have in Latvia is something they have hardly heard of, nevermind EV DO, the high speed wireless internet standard that Triatel offers and that will be capable of multi-megabit speeds by the end of this year.
If you have a Latvian GSM (LMT) phone, the coverage has been good so far, with Cingular popping up more often than not. It is possible to call US mobile phones of unknown network (such as the phone of a former colleague who moved to California some years ago), but not possible to send SMS.
So far the places we have been staying (imcluding a very cheap motel-type place in Hollywood) have had good free wireless internet or free internet (Ethernet line here in San Diego). I have used SkypeOut to make calls to US phones, but Latvia remains expensive (around EUR 0.20 per minute) so I have not made any Skype calls (also, there is a rather large time difference and by the end of the day here, it is the middle of the night in Riga).
Off on a day trip to Tijuana, Mexico today (Saturday). A day of sad remembrance in Latvia, the March 25, 1949 deportations.