Not only does MJ work good on USB1.1, using an old machine dedicated to the MagicJack device works much better than a new high speed computer running multiple apps.
My old HP mini tower computer XP SP3 delivers almost perfect phone service here in the sticks of east Tenn.
Ditto - worked just fine on a PIII computer with USB 1.1. However I have since added a PCI USB 2.0 card (because I needed more USB ports and it was cheaper ($5 via ebay) to buy the card than to buy a USB hub) and it works the same on USB 2.0 ports