Why does direct carrier billing not work with certain carriers for Google Play in-app subscription purchases?

I have implemented In-App Subscriptions with Google Play Billing API V2. Testing has been successful using Credit Card.

I do have issues with purchases made with Direct Carrier Billing though.

Here's what I have (testing with US-based carriers only):

• AT&T - works perfectly
• Verizon - untested just yet, waiting for a device to arrive.
• Sprint - getting an error that "Direct Carrier Billing is not available (IAI).
• T-mobile - getting an error that "Direct Carrier Billing is not available (IAI).

What's interesting is that making purchases of regular apps using Carrier Billing seems to work, the problem only lies with purchasing in-app subsriptions.

Ruled out all configuration, etc issues, as the error occurs once inside Google Wallet GUI (after hitting the Accept button) and it does work 100% of the time for AT&T.

Anyone has any clue what's going on with DCB and IAB for subscriptions on T-mobile and Sprint?

Source: http://stackoverflow.com/questions/14392664/why-does-direct-carrier-billing-not-work-with-certain-carriers-for-google-play-i

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