Help me find a non-contract data plan for an old iPhone?

Cultural Geek Girl

In short: a friend of mine has an old iPhone that hasn't had service on it for years. He needs to get service again. He's cheap and doesn't want a contract. He'd probably be fine with a pretty minimal plan. Advice?

My google-fu has been really weak on this: most places assume you want a new phone, and some of the solutions for pre-existing phones I've run into are basically hacks to get around a conventional phone plan. My friend is... a bit of a dinosaur. He's lived without any phone at all for the past year, since he moved back to California from Canada. He doesn't even know what generation his phone is... when I asked he said "uuuuuh, I got it in 2012. does that help?" He's bringing it in tomorrow for me to look at, but I'm not exactly the most tech-savvy person - the fact that I'm the one he goes to for advice is a very bad sign.

Essentially, what's the best non-contract plan for a pre-existing iPhone that you can just walk into a retail location somewhere and get set up? I know y'all probably need more information, but I figure I'd get this thread started and update it when I get more information tomorrow. Plus, you guys might know more things I have to find out that I wouldn't think of myself.

Thanks in advance.

hsu

Here's a few of the low cost companies that sprung up as subsidiaries of the major carriers.
AT&T -> Cricket Wireless
Sprint -> Boost Mobile and Virgin Mobile