The conversations I've had with Cisco around CUMA 7 boil down to this:
1. CUMA 7 will continue to support CUMC 3 clients until they release the CUMC 7 clients for Symbian and Blackberry. The conversation doesn't go any deeper than they will be releasing a 7 client for these platforms. I believe the CUMC 7 client will communicate with CUMA through the BES server and no longer require the proxy (for Blackberry-only deployments)... not positive on that though.
2. The Windows Mobile 6 Standard is what they have been having the best luck with. BlackJack2 and MotoQ9h to start with since that's what they developed the clients on internally. Additional models will be certified as they get beyond FCS. The developers have been complaining about oddness between phone models, between standard and professional, phones with sliding keyboards, etc. This inconsistency is why there isn't generic Windows Mobile 6 support and it's model-specific.
That's the extent of what I know that's non-NDA.