1 - Depends on your carrier and what your intentions are for wireless application management (push deliverables) and wireless backup of the handhelds (enabled by default on every user starting with BES 4.0 and above). Normal data charges shouldn't put you over any sort of standard limits, but some users could likely get carried away with MDS services (if you have them enabled). T-Mobile charges $10 extra for Enterprise provisioning over BIS usage.
2 - Read the manual and make sure that you have ALL of your ducks in a row. If you skip a step, then it will likely fail. If you login using the wrong account (domain administrator, for instance), then it will likely fail. I've never had a bad installation of the server - ever. And I'd say that 90% or more of all installation failures is due to the fact that someone didn't read or didn't understand the installation manual (and its REALLY easy to understand).
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