Issues with Sprint U301 USB modem (especially on Ubuntu Lucid)

These link say it all:
http://kerneltrap.org/mailarchive/linux-usb/2010/2/19/6257991

I'm doing some reliability testing to see what happens to the device if it loses
service.  With a connection up, I place the device inside a metal enclosure to
simulate the loss of network connectivity.

The device behaves as I would expect for the first ten to fifteen minutes (I
have not timed it).  The PPP connection takes a few minutes to timeout and die.
wvdial tries to dial a bit more and then quits.

The problems come after the device has sat idle for a few more minutes.  It
subsequently goes offline.  I am unable to revive it except by physically
disconnecting it from the USB port and reinserting it.

http://www.mail-archive.com/networkmanager-list@gnome.org/msg15988.html

It may be time to switch back to the U598 modem.