Sure, although you may reconsider when you see what some European hotels charge for wifi access. Skype has a promotion so that all calls to the US are free (not just to 800 numbers which always were) but if you have to pay $10/hr for wifi, it's not much of a bargain.
Get a decent calling card. For example, I have Cognicall's card which is 14.5 cpm from France or 11.6 cpm from the UK, works from payphones or the hotel room phone, and doesn't need any extra hardware.
If you're going to be spending a while in one country, see what the local calling cards cost. Friends in the UK tell me that you can get cards to call the US for under 5 cpm.
I have a little generic USB handset I bought on ebay. Works fine.
Note to Pat: Back when I had Vonage, I lugged my TA around on some trips, and it wasn't so great. I had to use my laptop as a router since the TA doesn't speak wifi, and even at places with wired access, you invariably had to log in from a web browser first. The TA and the cables took up a lot more space in my suitcase than my USB handset.