Many/most of the phones have model numbers ending in C or G. The Cs probably use Verizon (CDMA technology) and the Gs probably use ATT (GSM technology).
I had a Motorola G and ported my number over from my ATT account. I lost it. I emailed their customer service, who took a couple days to reply (the website said to email, no phone number for CS). The reply gave me a phone number, which I called, but after ten minutes I hung up and called again with a speaker phone because of the long hold time. After an hour or so, they discontinued the lost phone "to preserve the minutes."
I bought from their website a C phone, and after it arrived I called back to ask for the minutes and number. They said I don't have the phone or its SIM card, so they can't give me my lost minutes, and the number "was returned to the carrier" (I presume ATT), so buy new minutes and here's your new number.
Most of the minute packages they sell come with 90 more days added to your expiration date. Some add a year and one adds only 30 days. You can pay as much as maybe 50 cents per minute, but with the doubling feature and some frequently available bonus minutes, I have gotten it down to about 8 cents a minute. If you talk for 1 minute and 5 seconds, they deduct two minutes from your supply. :annoyed:
Their other company, Net10, sells minutes at ten cents each with 60 days added to the expiration date, so this might be good for you depending on your talk style.
After my current Tracfone uses up its minutes, I expect to switch to the new plan that Sprint and Wal*Mart are rolling out called Common Cents Mobile. This has two advantages for me: Minutes are 7 cents each for $20 adding 30 days service, $30 adding 60 days and $150 adding 1 year; and they round DOWN -- talk for 1 minute and 46 seconds and they deduct only 1 minute.

Sprint uses CDMA technology.