I've had the Skype unlimited North American calling plan for four years at $3/month. It permits unlimited calling to North American numbers from anywhere in the world. It also gives you an annual US or Canadian number for half price ($24/yr).

If you will be in any of the locations for long, I would go with a local prepaid sim for data. The international offerings by US operators are far more expensive.

As others have said, Skype is constrained in many ME countries as the monarchs have substantial interests in the telcos. They don't hassle yahoo Messenger and Google Voice as much. I take the latest US versions of the Skype and Yahoo Messenger installation programs with me and give them to friends and clients there to help them circumvent the restrictions.

There are so many wifi hotspots thoughout the ME now, I just head to one to surf the net and make calls on Skype, Yahoo Msgr or Google Voice. Their rates are similar.