Phone

How to get a phone
A smartphone is a necessity during your stay in Kenya. Everyone has one, though there are still landline phone users. The landline phone system is often limited to offices and homes. Hand-held portable phones are preferred due to their reliability. What you need to get is a mobile phone number and airtime.
You are required to avail an identification card or a passport when shopping for a SIM card. You may not instantly get an id card when you arrive so there is no harm borrowing a SIM card from a friend or colleague because people are well stocked in mobile phone numbers. But the easiest and quickest way is to spend a few more minutes when arriving in Nairobi airport. Once you are in the arrival hall you can buy a SIM card and prepay an amount to get you going.

Kenya has four mobile service providers namely Safaricom, Airtel, Orange and Yu Mobile. These companies offer both data and telephone services. They are all useful, however, Safaricom is the biggest mobile service provider in the market, controlling almost three quarters of the telecommunication industry. These companies have also rolled out mobile money transfer platforms which enable you to send and receive money with your smartphone. Safaricom has MPESA, globally acclaimed for its game changer in the mobile money industry. Airtel offers Airtel Money.

Topping up your airtime is hassle free. Airtime vendors are basically everywhere. You can buy airtime from your MPESA account as well. Communication has never been this easy.
It is just a matter of time, before you become familiar with the famous MPESA system; you can pay water and electricity bills, fuel charge and even your transportation fees using this system.
See a BBC feature article on Mpesa here (2010). and the system is continously being updated:

Safaricom eyes easier M-Pesa use with tap solution