Every landline in Zambia uses the area code system; you only have to dial it if you are calling outside of your area code.
The international access code for dialling outside of Zambia is 00, followed by the relevant country code. If you’re calling Zambia from another country, the country code is +260, but drop the initial zero of the area code.
MTN and Airtel are the most reliable mobile (cell) phone networks. If you own a GSM phone, you can buy a cheap SIM card without a problem (including at the Lusaka or Livingstone Airport). You'll need to bring along your passport to have it activated. You can then purchase credit in whatever denominations you need from the same company as your SIM; scratch cards range from ZMW1 to ZMW100. In Lusaka the best place to buy a cheap mobile phone is around Kalima Towers (corner of Chachacha and Katunjila Rds); a basic model will cost around ZMW80.
Numbers starting with 09 plus another two numbers, eg 0977, are mobile-phone numbers. Mobile-phone reception is getting better all the time; generally, it’s very good in urban areas and surprisingly good in some rural parts of the country and patchy or non-existent in others. Don't count on any coverage inside the national parks.