On my most recent trip to Prague, I needed to secure relatively hi-speed internet on a month by month basis, without waiting the 2 weeks required to DSL your home line. A home line that I didn't even own. Before my arrival my wife got a vodafone cellar modem for me, which worked right out of the box and came with a month free trial with deposit. This sounded exploitable, except the 2gb limit (in a month) ran out fast, and from there Vodafone requires 6 month contracts. I did a little research and found that O2 has an English speaking store and a day by day prepay contract. Awesome.
I get the modem, run to my soviet-era panel building and plug the modem in. Nothing. Nothing at all.