I currently have an ex720 from sprint, originally for my macbook pro. Ever since I purchased a mb, fully realizing it doesn't have an expresscard slot, I ordered a usb adapter for it. Worked right away upon plugging it in.
BTW, hope you know verizon secretly caps your monthly bandwidth allowance. Well, not really cap but they'll just terminate your service if you go over 5-10 gigs.
as far as usb devices go, check out the 3gstore guys like the post above.