T-Mobile started pushing out an update to the Android Market which allows customers to choose their billing method for paid applications.  Rather than using Google Checkout, users can opt to have these costs added to their T-Mobile account.

If you are a T-Mobile customer, you can expect to get your update sometime between now and the end of the month.  Don’t look for any specific notifications on your phone though, this ‘invisible’ update only applies to the Market and not Android as a whole.  You’ll have to log in and attempt to purchase an app to find out if you’re updated.  As of right now, only US currency is supported in the new carrier billing but Google and T-Mobile have committed to a work around to convert Pounds and Euros into US Dollars.  Sprint is expected to offer a similar service for their Android handsets in the future.