How does T-mobile prepaid work?

So I'm thinking about getting T-Mobile's prepaid plan for 30 dollars a month. When I do that, what kind of overage fees are there? Also, do I need to buy a phone outright, or can I pay per month for an iphone? Could I bring a T-mobile phone with me to get it activated?

I have the $30 plan, for several years since my 2 years ran out.

You can bring any Tmobile or unlocked phone that uses GSM network, and use it on Tmobile. I changed phones by buying one from craigslist.

You will get a text when you are close to getting a voice or text limit, and you will get a message that the data limit has been reached. You can then change your plan for that month if you simply can't abide by the limits.
http://how-to.t-mobile.com/overage-protection/

1500 is a lot of min and texts, and i have come close but not over. I don't live every min on my phone though. I only use the data to look up a number or check Maps or maybe kill time waiting for someone. Otherwise, i can use Wi-Fi at home or out.

I have been pleased with the amt of service for $30.

I do not know much about a T-Mobile prepaid plan, but I do know that you have to bring your own T-Mobile device or purchase one at full price (up front). You can't make payments.

We have been happy T-Mobile customers for over a decade and highly recommend them. Their customer service can't be beat! There have been issues but they have always been addressed to my satisfaction.

Since you are worried about overages, I thought I would tell you that you can get a Simple Choice Plan (no contract, month to month) for $50 a month. That includes unlimited calling, unlimited texting and unlimited data (with up to 500 mb of high speed data).