my 5 bars only sometimes 2 will appear on my cellphone

There's not much we can do to help. There can be any number of factors affecting your signal reception, from geographic location to a plain old brick wall. If you have poor signal reception in your area, you can get a signal extender directly from T-Mobile (it's free, aside from a small deposit) that might help you, but these aren't things you can carry around everywhere so it will really only be useful at home.