I came from Koodo and they use both AT&T and TMobile (at least did when I was there). I had to do the same thing on my Koodo plan and manually select a network occasionally when locked to one or the other network with a weaker signal.
My experience in the US is that unless you are in a city center the TMobile service is not very reliable. I generally manually force my phone to be on AT&T when in the US and have a much better experience.
Mine shows 8.5GB $50 and 30 day plan $10 in the transaction history. In the "My Data & Add-Ons" section there are 2 data buckets shown with the amount used: 1) 2GB at 3G Speed2) 8.5GB at 3G Speed Hope that helps.
