Phone for short US visits

My mom has a GoPhone through AT&T. She bought it 2 years ago and put $100 on it and I believe that she still has a remaining balance that she is using. I do recall that she may have said that she needs to put more on it after the first year, but I'm not sure.

ETA: I just had a look and the $100 she put on it was good for 365 days, after that she put another $100 for another year:

I have an old Virgin US PAYG phone & I just reactivate it online, get a new number assigned to it & top it up $20 which will last me for when I visit and if I need more credit I just top it up while I'm there. I've not had any problems other than having to remember a new number each time.

My mother also has a Virgin Mobile phone, and tops it up once a year.  I think it's either $100 or $120 she puts on it.  She's never lost her number, no matter how little she uses the phone during the year.

My mother also has a Virgin Mobile phone, and tops it up once a year.  I think it's either $100 or $120 she puts on it.  She's never lost her number, no matter how little she uses the phone during the year.

They may have changed the PAYG from when I purchased mine in 2006.