I have found Magic Jack to be reliable. I have even used it on cruise ships. They want $5/minute for cell usage... but internet packages run about 50cents/minute. However, on the boat the bandwith is barely enough for the magic Jack and it isn't real stable. (but works well enough to just ify the cost)

You do need to take the Magic jack with you... and a cheap phone handset, or you can use a headset with a microphone.