You should get charged by T-Mobile USA for every MMS message that routes as such through their MMS proxy (for those of use who have to use the proxy).

For my N900 on T-Mobile USA (Washington DC), I have to use the proxy as the standard T-Mobile internet access point won't transmit MMS messages from fMMS. So I expect to see MMS charges on my bill for each send/receive.

It's possible if you are able to MMS through your default T-Mobile Internet access point (that would be wap.voicestream.com or internet2.t-mobile.com without a proxy) then I guess it would just show up as data and charged as such.

Since we're talking about it, I noticed that I can web browse and email just fine on T-Mobile USA 3G and EDGE using my Proxy enabled T-MoMMS access point.

Is there any noticed badness to using the MMS access point full time instead of the default T-Mobile internet one, cause I haven't seen any ill-effects yet.