Hi kelsbells64,
Because the hardware for the modems is different, they would need to be seperately uninstalled and re-installed each time you wanted to switch between them, so this is not ideal as you say.
I'm guessing the only reason you want to do this is to share the usage from both contracts, is that correct? If so, then what I would recommend doing, is simply swapping your SIM cards, rather than the modem itself. So long as both SIM cards are on Contract Mobile Broadband, they will work in either modem. All you need to do is pick your favourite modem (I'm guessing this will be the K3520 since that's already installed and working), and when you're ready to switch half-way through the month, simply remove your SIM card and replace it with the one from the other modem.
I trust this solution works for you? Let me know if you have further questions
Jon
eForum Team