thank you, I think I got it covered. I was impatient, and called ST customer service, and figured out I can use my att phone, call her phone, when it goes to message, I press *, then I enter the voicemail account(her number again) with # sign, then her voicemail password with # sign, and get the messages. I think this will work OK for us.
I found the voicemail password(which I had forgotten, of course) by using her phone, going thru the settings on her voicemail, and turning on and off the requirement to enter the password.
It was rather difficult for me to find out there were no options to activate the phone in Mexico. This is something that should be easier to find out on the website. Good luck and I do appreciate your reply.