We have done so for the past year+, and it works fine. We use a mix of user and device cals (same price) but device cals allow multiple users to work on the same device (cal), without each user needing a license counted for them.
SBS has some drawbacks that has made me switch to full server, full exchange, etc. as our practice has become more dependent on a functioning server on at least a 18/7 basis (and 6hrs isnt enough time to build and restore a backup server box). The main issue is that SBS only allows for one domain controller. If one wants redundancy of the domain controller and the server state on a second server, we had to switch away from sbs.
Using the included fax server works ok, but has some limits. The main one we found with ac2 and 3.x was that printing letters to the fax printer often (but not always...) fails to be 'saved' in the imported files section. One gets around this by printing in some way that saves the file, closing and reopening the saved/imported file and printing that to the fax server. Second, if you have a letter, the encounter note, and the demographics sheet being printed (in other words multple reports for one fax), each is considered a seperate print event and you end up sending multiple faxes. We get around this by printing to a pdf creator, then adding the second, third, etc, parts (also printed in pdf) as merging onto the end of the letter pdf, and then once the final pdf is built, printing that to the fax server. We save the letter(only) pdf and then import it to the imported files section and delete the html letter (which almost always hass formatting problems after its saved by ac). You can not use the provider database in AC to pull up fax numbers, but you can use public and global, as well as private, contact lists from outlook/exchange for the fax contact list, for the SBS fax server.
good luck!
