Meanwhile units in Malawi will go to Eaton Towers, a person with knowledge of the deal said on Wednesday.
Mobile operators such as India's Bharti have been selling masts to specialist tower firms and leasing them back to cut maintenance costs on a continent with poor access to electricity and shoddy roads.
The Tanzania sale will include about 1,000 towers, said the source, who declined to be identified because the deal has not been concluded. The source did not say how many towers in Malawi would be sold.
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Bharti has said it would sell 3,500 towers across six African countries to Eaton, and 3,100 masts in four countries to Helios. It has not given details on the countries involved.
Eaton chief executive Alan Harper declined to comment on the details of the sales. Helios and Bharti both declined to comment.