A techie friend just introduced me to Zimbra, he has recently switched his small company from a hosted exchange solution to a hosted ZimbraCS solution. In the UK you can get a hosted Zimbra mailbox for £3.99 per month, for this fee you get an Ajax web client, seamless integration with Outlook and many other webclients. Mobile messaging, some of the solution providers offer support for Blackberry's some are still working at it. You enjoy shared calendars and a lot of the other collaberative features Exchange offers without the serious support overhead.

Zimbra is still fairly new but has some serious VC muscle behind it so watch this space. My company Redline Software made a concious decision to avoid Exchange due to it's support overhead and the horror stories that have circulated about corrupt database files and elongated periods of outage were also driving factors. Instead we opted for a simple solution called Mailenable that did a great job as a Pop3 server and integrated nicely with Outlook. We lost out on the collabarative features of Exchange but we were a small company so collabaration wasn't a big issue for us. We are still using Mailenable but are evaluating ZimbraCS.