I paid about 100 odd dollars for about 130 minutes on pay as you go (can't rememember exactly the amount) and they last about 2 years or so.
I know when I bought it that US (I am based in Europe)users had to have a bill, I was told it was due to some legal issue, this may have changed now.
I was on holidays in Canada a few weeks ago and it worked fine for me in Algonquin National Park.
The unit is very rugged and weighs about 260g.
When I was buying I looked at Globalstar (which spot uses) but they where having issues with their satleittes but I think new ones have been placed in Orbit.
I also looked at Thuraya but it does not work in North America.
Immarast is the only system that has true Global coverage but the unit and running costs where twice that of Immarast.