Maybe I can sched some light on this one. While tinkering with my BB (8820), trying to get it to work on the wireless here, I noticed that it couldn't look up the BES's hostname (the one that is shown in Wifi Diagnostics). Tracing it on the network, I noticed that it is in fact not looking up the hostname but instead is looking up:
hostname.MagicRudyAPN.rim
Why it appends that 'MagicRudyAPN.rim' to the hostname is a mystery to me. All that does is break name resolution as the name can't resolve like that on our network (I had to specifically create the MagicRudyAPN.rim zone in DNS and define hostname.MagicRudyAPN.rim in there to get the BB to recognize the BES server when connected wirelessly).