Thanks for the post, Neil...I am a mac user, but do understand that the Iphone isn't in the cards for you right now.
Blackberry, however, even though it may not be in your eyes a viable option, is VERY widely used with corporate, fractional, and other charter type organizations. I don't think it's going away anytime soon, and would serve your customers well. One suggestion: Poll your customers, see what the response is, and then you can offer seperate purchase options for PDA support. If Blackberry users want Blackberry support, then they'll pay for it (I know I would upgrade) and there you can generate revenue for the cause.
Please don't give up on Blackberry. Too many organizations are standardized on it.