Cingular/T-mobile Prepaid: Misinformed or illtrained sales associates?

I wanted to get a prepaid plan for a guest who was here in US for a short duration, I had my own phone (GSM, new one from cingular and other Sony erricson that was unlocked) i visited T-mobile and the sales associate (in San mateo) said that minimum was $50, since I did not need it for that much I declined and went to cingular in fremont, ca. There sales associate said that the minimum is $25 if you are getting a new SIM card and since I was in a hurry i just signed up.

After a month, I am realizing that I may have been misinformed by these sales guys , I can see starter kits available for as small as $10 from walmart, ebay and other outlets.

Well, knowing is key to these things, idea of using prepaid itself was so new to me, I just got too excited that I could get a SIM card for $25, jumped into it Sometimes even time is a factor, you dont want to research too much when you need something right then.