Mobile phones work on a GSM system using Siemens-Motorola kit that is compatible with Western systems. Probably the most reliable supplier is MagtiCom, a joint venture with the American company Telcell. The main alternative is Geocell.
Dialing is not simple: mobile codes are 877 or 893 (Geocell) or 899 (MagtiCom) - 77 or 99 from abroad; pause after the 8 and 99 for a tone. To call a Tbilisi number from a mobile, dial 832 then six digits; to dial any other fixed line, dial 8 and the code and the number.
Bring your own phone, and buy a SIM card for GEL10, including GEL5 credit, from a corner shop. In truly remote areas such as Khevsureti there's no mobile (or fixed) phone coverage, but some satellite phones are available, at GEL9 per minute.
Georgia's country code is 995, and the code for Tbilisi is 32, so that from most countries you'll dial 0099532, followed by the number. Other codes are 222 for Batumi, 231 for Kutaisi, 293 for Poti and 250 for Telavi; calling from abroad, however, you must change the initial 2 of these or any other town codes to 3.
Special numbers include:
Long-distance operator 07
Directory enquiries for Tbilisi 09, elsewhere 05