Select Mobile Devices (Inbound SMTP)

We have a few users (Blackberry) that will check mail via IMAP and send via SMTP (same server). We currently have the inbound SMTP restricted to a trusted SMTP service only. I noticed a relay exception for authenticated users. Would this allow these users to connect or do we also need to include the service provider domains (e.g. *.verizon, etc.)? We do not have enough users to warrant a BES server so we’re getting creative. Fortunately for other users, there is Lotus Traveler!!! Thanks in advance.