Used to have the same usb modem a while ago and it would suffer 'drop-outs'. I had to log in to my ISP to connect to the net so invested in an Ethernet modem. This meant that I had an 'always on' connection and was much more stable. It doesn't need drivers but has to be set up to your ISP's configuration. Something like this; click here .
Don't know why the DNS addresses disappear though.