I can't say for the Sprint card, but my ATT Communcation Manager has a setting to allow for multiple connections (see jpg). It started when I upgraded to v6.10. It wouldn't disconnect me unless I clicked on OK (or Cancel....) but once I set the CM to allow for multiple connections, I don't have this problem any more.
We had some users with the same problem. Here was the fix given by Sprint. I have not tested it myself
In Smartview, go to the Tools->Settings Menu and look for Rules EngineÓ. If you donÕt see that tab, close the app and reopen it again as many times as necessary.
In that tab, uncheck the first box Use Rules EngineÓ.
The issue is that the air card software thinks NC is a new connection as if you plugged in an Ethernet cable so it thinks another Internet connection exists.