I take both my laptop and our mobiles every time we visit the USA. For the laptop I usually use it free in hotel rooms if offered (luckily we get it free at WDW because of DVC). Then we just plug it in and it works.
For our mobiles, we just use our regular UK sim card and use what ever network our phones connect to. As for price, it can be expensive (especially if you have a smart phone and don't turn the data roaming off!!), but we always phone up O2 before we leave and have the cheaper US rate put ont he phone for a month (it is a minimal charge but makes the minute/media message cost cheaper.)