We've been calling the HTC Magic the T-Mobile G2 around these parts because well, to us it already made sense. The HTC Magic was codenamed the Sapphire which was supposed to be the G2. And since Vodafone (and not T-Mobile, whom have the 'G' rights) is carrying the HTC Magic outside of the US it won't receive the "G" moniker..yet. But once it hits T-Mobile USA? We think G2 would be the safe assumption.
Engadget has dug up these slides (during the offline Gmail presentation) of a HTC Magic with T-Mobile US branding. So yeah, we do think the HTC Magic is going to be the G2. Time will tell if there'll be any unique tweaks for us stateside.