I've been on the $30 plan for almost a year now with a WP7. I am generally happy with it but it is a bit of a change from postpaid accounts. Here's what I have learned:
Not only is there no monthly bill mailed to you, there is no detailed billing period. When you log onto mytmobile.com, you get the number of minutes and MB of data used so far that month, and that's it. No detailed breakdown of the calls you have made and no mention of texts at all. Just 2 boxes with minutes used and data used. And when the current month is up and you renew for another 30 days, everything is wiped out and reset to zero. No historical details are available. If you want to know how many minutes you used 2 months ago, you are out of luck.
Autopay is flaky. The plan is a strict 30 day plan, not a calendar month plan, so your renew date is almost always different. My plan renews in the first week of the month, but never the same day. My plan renews between the 3rd and 6th generally. When you set up autopay, you have to select a date to pay from a drop down menu. But it doesn't let you choose specific days, like the 1st or fourth day of the month. It makes you pick days before renewal. When I used autopay, I chose Pay One day before Renewal. The second month of autopay, it flaked on me. I got a text the day before saying my CC had been billed. At midnight, I got another text saying my 30 days were up and I needed to refill my account. Apparently, there is a lag involved when using Autopay. It took them until 8am the next day for my automatic payment to be released and become available. I wasn't able to make or receive phone calls or texts between midnight and 8am. I got rid of Autopay after that.
You can add money to your account with a debit or credit card at any time and in any amount over $10. You don't have to add money in multiples of $30. You can add $30.10 or $88.50, it doesn't matter. After getting rid of autopay, I started adding $62.00 at a time. That covered 2 months of renewals and an extra 20 minutes worth of calls if i ever went over 100 minutes in a month. I never came close to going over.
You get a warning text every month 3 days before your renewal. If you don't want to keep extra money in your account, it is a handy reminder.
There are no monthly fees or taxes on the plan. If you have $30 in your account, it just takes the $30. They do charge me the NJ sales tax of 7% when I add money to my account. So if I add $30, my CC gets billed $32.10. I never use them but I assume they also charge a sales tax when you buy the prepaid refill cards from T-Mobile or some other reseller.
That's pretty much all there is to it. If anyone has any other questions, just ask.