We currently have a similar problem on O2 in the UK with accessing the BIS over WiFi from anywhere. I'm told it may work over their Hot-Spots but haven't seen this for myself.
It is possible for a carrier to restrict access to their BIS server by looking at the source IP address and only allowing their own address's through.
So you could access the BIS if your were at one of their Hot-Spots but not from you home or work.
If you are connecting both of these routers to the same internet connection and one works and the other doesn't then it has to be router configuration.
BlackBerry Bold2 9700 / 184.108.40.2068 / BESx
Blackberry Playbook 32gb WiFi / 220.127.116.110