I am with T-Mobile and I have Windows Phone 7.5 Mango, Nokia Lumia 710. I am very happy with it after using Android and Blackberry. As you may know, this phone is not being supported with Windows 7.8. Anyway, I have been using the "internet sharing" feature with my macbook pro and it has been working great. I have not been getting charged for it. I have the Unlimited 4g data plan with 500 minutes and unlimited text and my bill has not gone up since I started using the internet sharing. Do you have any idea if T-Mobile will start charging me for this? Can they charge me retroactively for using this feature? I want to continue using it and will be for it if it is reasonably priced. Any thoughts?