OS 2 Beta gives every indication that the Bridge will be fully supported going forward. I wouldn't be at all surprised if native email will function over the bridge or tethered connections when wifi is not available. This being the case, the usual carrier plans and fees fees would apply to non-wifi connections. If you now pay tethering fees for bridging, then there will also be extra fees for native email.
Originally Posted by mjs416
Disclaimer: this is pure speculation - nobody really knows how native email will work.