I first got my Captivate Glide brand new, off-contract from AT&T. I paid full price for it thinking I could use a T-Mobile sim card in it. Due to limitations with TM's 3G/4G in my town I opted to instead use a prepaid AT&T plan/sim. The AT&T rep said it would work since AT&T offered prepaid with some of their smartphones. - WRONG!
Like your friend I could only get talk and text, even though I had added data to my AT&T prepaid plan/sim. The AT&T rep literally spent two days on the phone with cust service trying to get my data to work - which it never did. Apparently AT&T uses different towers for their prepaid service and those towers are lower priority and more sparse than the premium towers. So depending on where you were in relation to the prepaid towers the data would work (albeit poorly) at times - if close - or not at all - if far. The prepaid towers are apparently few and far between compared to AT&T's standard towers. (Actually my data did work for about 1/2 a day, then the one and only AT&T prepaid tower in my area went down which accounts for the sudden interruption and end of data on my brand new CaptGlide.) This all sounded plausible given my 1/2 day with data working and subsequent 2 days without data working at all. Long story but this is how I had the exact same problem with my Captivate Glide as your friend.
I opted to just get a standard (more expensive) AT&T account for now to make the data issue go away. Captivate Glide works famously now and so does the data. So maybe their issue is that they're using a prepaid AT&T plan/sim. If they're using a regular AT&T account and sim and have data then my verbose experience probably won't help you.
Good luck.
