Switching from AT&T post-paid plan to pre-paid: Is it possible, any gotchas?

[$tevie]

I switched from AT&T post-paid to prepaid with an old 4s that I'd bought from swappa or some place like that (been a while and my memory sucks). As long as it's an AT&T version of an iPhone, you are fine. I can't recall if I had to change my number or not, sorry. I don't think so.

However, I noticed that the SIM on the SE says it's specifically for AT&T prepaid so I'm thinking that you would need to get and activate a new SIM card to go back to postpaid.