Originally known as "MSI Cellular Investments", the company began operating in 1998. In January 2004, the company name was changed to "Celtel International". In April 2005 the company was acquired by and became a subsidiary of the Mobile Telecommunications Company. Celtel now spans over 15 countries in Africa with over $750 million in investments.
Celtel operates in the following countries:

It currently has 20 million subscribers -
In June 2007 Celtel's One Network was extended to Gabon, the Democratic Republic of Congo, and Congo.
The One Network will automatically activate upon crossing the geographical border into one of the six countries with no prior registration or sign-up fee. Celtel says it is moving towards a seamless network in all 15 African countries in which it operates. 
In June 2007, Celtel International announced plans to add three more Celtel country networks to its "One Network". The additional countries are Malawi, Sudan (where it operates under the Mobitel brand), and Zambia. This further expansion would bring the coverage of One Network to nine of the 15 African countries in which Celtel operates. 
On September 2007 Celtel's Parent Company MTC Group adopted a new name Zain (Arabic for ‘beautiful, good and wonderful) unifying it's different brands in 22 Countries.
In Africa the Zain Group will continue to trade under the Celtel brand.
On October 2007 Celtel International Acquired a 75% stake in Western Telesystems LTD (Westel) from the Ghanaian Government for $120 million US Dollars 
On 22 November 2007 Celtel doubled it's One Network countries from 6 to 12 countries by adding Burkina Faso,Chad,Malawi,Niger,Nigeria and Sudan.
Celtel currently has 24 million subscribers in 14 countries of Africa
Celtel will restart rebranding into Zain in April 2008 and will expand its ``One Network" across its 22 Operations by end of June 2008. 
On 1 August 2008 the Celtel brand across Africa was dropped by the parent company Zain Group and all the operations rebranded to Zain