On the prepaid plan, does the $30 or $50 you put in, does it expire after 90 days?
I know with pay as you go, for $100 it is good for up to 1 yr and you get gold status.
Does it apply in Prepaid plan like the monthly $30, $50, $60 or $70 plan?
The Monthly Prepaid Plan is just that, monthly. You have to pay the $30 every month to continue to have service, there is no option to pay more and have the plan last longer. If you go over your $100 minutes with the plan, additional minutes are charged at 10 cents a minute (so long as you have money in your account to cover the cost of those minutes). If you put $100 in your account, they will just use it to pay for 3 months of service, taking $30 out every 30 days (provided you don't otherwise spend the money, such as on extra minutes).
The plans you are talking about vary the number of minutes and the time you have to use those minutes based on the size of the refill card you buy. For example, with the T-Mobile Pay As You Go, if you pay between $10-50, the minutes you buy will last 90 days, and if you buy the $100 card the minutes will last for one year. The disadvantage to this is that when you run out of minutes, unlike on the Monthly Plan, you have to purchase a new plan, no matter how much or your 90 days (or 1 year) that you have left. Your plan starts over, based on the amount of the card used. Even if your minutes had lasted one year previously, if you don't use the $100 card then your minutes will only last 90 days. Also, T-Mobile does not offer this type of plan for data -- all the data plans are Monthly.
Hope this helps.