The biggest provider is Czech telecom - CTc.

International calls from the Czech Republic: prefix for international calling from Czech telephones is 00 followed by country code.
Ona unit in local calls: 3 Kc
Telephone cards can be bought at larger post offices, airports, railway stations, metro stations, big department stores,kiosks and hotels. There are several types of these cards, usually from 50 to 150 units (50 unit card costs 200 Kc, 100 unit card is 400Kc). You can also buy special long-distance call cards from an Internet Provider called Volny. These cards are available at all post offices.

AT&T Operator: 00-420-00101
MCI Operator: 00-420-0011
Sprint Operator: 00-420-87187
Bell Canada Operator: 00-420-00151

Note on Cellular Telephones:
Your cell phone is most likely 800MHz. In the Czech Republic the standard was 450MHz, therefore there was no chance that it would work over here. But more recently they have changed to GSM and operate between 800 and 1600MHZ.

The main providers in the Czech Rep. are Eurotel, Paegas and Cesky Mobil. The connection fees are very expensive. You have to purchase the phone, a phone number and the connection.

If you want to use a foreign mobile phone in the Czech Republic you have to first remove the international restriction on the phone in the country of origin.