Czech mobile networks (Prague)

Hi everyone!

I'm moving to prague in 2 weeks in order to start a six months internship and I would like to ask you for some advice regarding mobile networks.

I will have to buy a mobile card from a czech mobile operator in order to communicate with people I'll met there and I want to know which one is the most popular among prague citizens. I want something with good mobile tariffs, free sms between users of the same carrier and internet fixed tariffs.

Thank you in advance for your help!

Any other tips for this new expat are most welcome.