Skype bases your call pricing based on your GEO located IP address, no matter what calling plan you have.
A good alternative is Google Voice. Unlimited US calls and texting, along with a free number in most US markets.
Problem is you need another number for Google voice to call you.
You can use IPKall for a free number, or Gizmo 5 on your PC.
I have no idea what to do with the Skype information. It seems incomplete. Google voice and Callclicker are not available in Mexico.