That does tend to be the case. Blackberry want you to tie in with a provider on a contract - hence no real chance of a pay-as-you-go for the emails.
I'm actually going the other way! I have a contract sim that I'm going to plug into a BB - but I won't be using the emails etc. - just the phone!
Reason? My present phone is used mostly on Bluetooth and the battery does go flat very quickly. (Not quite sure why. If the phone is in my pocket and I'm away from my Bluetooth, the battery lasts a heck of a lot longer.) But the BB I've got has a much better battery life; hence the 'conversion'.