Travelex Phone Card (forget who provide it for them) is the best one we've found for using. Its a toll free access number so no problems to call it off the room phone - at WDW hotel anyway.
As has been said, never phone internationally from the room, prices are from Mars and then AT&T add on a 55% surcharge - WDW hotels anyway.
If your planning on using your mobile a fair bit, add on a bundle.
We take our mobiles but never use them, simply for anyone to get in touch with us if they need to. For when we are there, we get a couple AT&T sims before we go out, and buy credit online using mypinzoo, again before we go out.
With the free wifi - your best off emailing using that. The last couple years I've added a data bundle on for going to the states to email a couple friends back home (never bother with facebook or checking whats been happening news wise). It works out a damn lot cheaper adding a data bundle on than texting when you think of how much you can say in a text and cost per text compared to your data allowance.