Sorry that I am too late to help the OP, but I found the data SIM card offered by T-Mobile worked great in my Android unlocked smart phone (Verizon Samsung Note II). Cost the equivalent of $10 for 250 MB of data, and activation was a snap with the help of the T-Mobile store employee. The same can't be said for Vodaphone, who sold me a card that could not be activated; they refused to refund my money, so I need to take that up with Visa.

Unless you speak good Czech, I'd stay away from Vodaphone. Few of their staff spoke competent English (in a major Prague mall), and the text messages you receive directing the activation process are all in Czech.

I don't know whether a combo data/voice card is available in the Czech Republlic, since I didn't ask. But the A1 card I bought in Vienna for 10 euros gave me both 1 GB of data and something like 1000 minutes of voice. Unbelievable value there.