Nothing to stop you. You can use Isolated Storage, XML, etc. But, IMO, WP7 is currently targeting personal use, not business use, so a DB isn't as important. I'm still seriously considering getting a WP7 phone when available, but am holding off final decision to actually see the available devices, purchase costs, and service plan costs.

>So much for my interest in Mobile 7. I was under the mistaken impression that it was an improvement compared to mobile 6. At least with 6 you could develop some business apps.