Thanks to everyone who replied. There were some very informative comments. As for the whole "Dude, it is vacation, leave the phone home" discussion, there are always two sides. I use my mobile service a lot here in Europe. I like statistics, that is one of the reason I try to tag/login to any places possible using my mobile. Let it be Facebook/Twitter/4square. That is also how I keep all my friends updated. And I don't want to miss that opportunity while we are in the US. From what I got out of all the comments so far is that Verizon is much more preferred than ATT, and that some users around the SF/LV/LA area were also using Virgin Mobile or Sprint devices. I also don't want to spend that much, so I'm looking for the possible cheapest option available. Which looks like will be a prepaid SIM card with a months worth of data, if I get the device from somewhere else. I was also unaware of the different 3G frequencies, which makes it even more complex.