wireless modem won't connect to stream

Hello, I have a US Cellular UM175 modem and a MBR900 router setup that two laptops receive wifi from.
Scottrade has a java based application that streams selected ticker symbol trade times and price continually as a streaming page.
This setup has worked for two years but the other day it refused to stream the data. When the streaming quote page loads, it displays a "snapshot" of the pricing and times but does not update. There is a connection status indicator that shows "not connected ".
The scottrade support says it's either a firewall or modem issue. And of course USCell says it is scottrade.
Nothing has changed except I updated to Firefox 4.0 and since went back to 3.X.
I brought the laptop to work and plugged into a LAN port and the stream connects and works fine.
At home I did skip the router and plugged the modem directly into the computer and it still refuses to connect to the streaming quotes. The internet works fine.
So the question is: do cell companies to software or firmware changes to modems unknown to the user and is it possible this is what has happened.

Also I read somewhere to type www.microsoft.com:443 into the address of the browser to check port 443 and it comes back unable to load on BOTH the modem and LAN connection so I do not believe it is the windows firewall. www.microsoft.com:80 works fine to MS

Neither Laptop will connect, one is an older XP SP2 machine and the other is a newer Dual Core Win7. They both have Avast! AV and connected last week using the cell modem.

Any help is appreciated

 

Thanks Tony, So far that is my suspicion also but they will not admit it.
Next I plan to take the laptop and modem to another area and connect to another tower to be sure the local service router is not jazzed up.