There are three major mobile operators using the GSM standard, their coverage is very good (except in some remote and mostly uninhabited areas). If roaming with your own operator seems too expensive or if you want to have a Czech phone number, you can buy an anonymous prepaid card from one of the three major operators. However, the pricing systems are usually quite complicated and it may be necessary to do some research to find the ideal solution (even with prepaid cards, operators offer different systems, including various additional ‘bundles’). GPRS and EDGE are widely available, support for 3G networks is in its infancy (O2, Vodafone and T-mobile, mainly in Prague). The fourth operator (U:fon) uses custom standards and you have to buy special equipment from them.
There are still a few phone boxes, but they are gradually disappearing since the advent of mobile phones. Some still accept coins, but most require a special prepaid phone card.
You can call the emergency numbers from any phone (even without a card) free of charge. The universal emergency number 112 is functional and you can use it, but you will only reach one operator who will have to contact the real emergency service for you. To save valuable time, it is best to call directly the service you need: 150 for the fire brigade, 155 for medical emergencies and 158 for the state police.
Wi-Fi is available in many restaurants and most cafés, especially in the larger cities. In particular, all branches of Starbucks, KFC, Gloria Jeans Coffee and Costa Coffee offer free access. You may need to ask a waiter for the passphrase. There are also a few street access points and some parts of the city (e.g. Prague) offer free wifi access for all. However, this coverage is usually very slow and unreliable, and you may need to create an account (via a web browser and the page you are automatically redirected to) to use it. There are also several internet cafés in most major cities.