T-Mobile is rolling out carrier-based billing for the Android Market, as promised. Customers are getting the option in waves, and all users will be upgraded by Dec. 30., though, there’s no notification process. Upgraded users will just see the “Bill my T-Mobile account” option (pictured) when they try to make a purchase.

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Carrier-based billing is currently only available for apps that can be bought using U.S. dollars; T-Mobile and Google (NSDQ: GOOG) are “working on a solution” to convert Euros and Pounds to dollars. U.S. currency restrictions aside, this is good news for Android app developers, since the need to use Google Checkout (and a credit card) has been cited as one of the main reasons hindering them from making real money from the Android Market.