I use bluetooth when doing anything like that. I couldn't imagine trying to sms or dial a number while cycling. As for a replacement phone, there are plenty that have most of the features you're looking for. Just go to a store and look at them. You can get all the advice you want from a forum, but since your case seems to be a special need on how it holds/handles in your hand in extreme conditions, the only way to be sure it to hold it.

Also, you probably won't find many people with advice on other phones here, since most people here are here because they have an N900 and are happy with it. I haven't bothered keeping up on every new phone release since I've got the phone I want now. I suspect most others here are in a similar boat.