As an avid user of mobile email I have over the years used various devices. I started with a Windows Mobile 5 O2 XDA II and then moved to an O2 XDA Mini. Whilst both of these used Active Sync to get my Microsoft Exchange email, the user experience wasn't very pleasing. The devices where slow and at the time data costs where quite expensive.
I have since moved to a Nokia E65 with Mail for Exchange installed and then onto an Apple iPhone 2G. One device I haven't used much is Blackberry. Mainly because of cost and also because I cannot see the point of it. Blackberry devices are expensive, cumbersome and tricky to setup.
We have setup BES (Blackberry Enterprise Server) and BPS (Blackberry Professional Server) and had a few nightmares with both of them. Add to that the BES and tariff costs, and it quickly becomes uneconomical to roll out for a small business. All of the other devices which support Active sync make more sense. Active Sync is included free with Exchange 2003 and 2007 - all you need is the right mobile with a good data tariff.
I was never really a fan of Apple machines but since moving to an iPhone I am completely hooked. As fanboys say "it just works" and with a correctly configured Exchange server it certainly does. Also, with the iPhone tariff from O2 having unlimited data then there is obviously a business case for using these phones in a business environment. As of this week Apple are releasing iPhone OS 3.0 which has the added function of being able to wipe the device remotely if it is lost or stolen.
This has been one of the selling points of Blackberry and now the iPhone will have it. This is only available for Exchange users but other email users can use Apple's MobileMe Service to wipe it remotely.
Time will tell on this but I am seeing more companies move to iPhones and not even considering Blackberry.