Motorola Inc is close to selling most of its wireless-network equipment business to Nokia Siemens Networks for $1.2 billion, a source familiar with the matter said on Sunday.

Nokia Siemens Network, a joint venture of Finland's Nokia Corp and Germany's Siemens AG, would buy Motorola's network unit under the deal, which could be announced as early as Monday, the source said.

Motorola plans to keep its iDen technology, which works for walkie-talkie types of communications, the source added.

Motorola, which has been losing market share in cellphones for years, is splitting into two units: one comprising phones and set-top boxes, and the other its enterprise and network equipment business.

NSN was in the running last year to buy a larger chunk of Motorola, before the U.S. group decided on the split, sources close to the situation told Reuters at the time.

NSN also tried last year to buy two separate units of bankrupt Canadian telecoms equipment maker Nortel Networks Corp, but was trumped on both occasions, once by mobile networks market leader LM Ericsson and once by Ciena Corp.

Earlier this month, one analyst questioned NSN's move to buy Motorola's network assets, which are mainly based on the GSM standard, rather than on the Nortel CDMA and LTE-standard assets that NSN tried to buy.

GSM is the world's most widespread wireless standard but CDMA is prevalent in North America and parts of Asia.

Motorola declined to comment on the news, which was first reported by the Wall Street Journal. The source is anonymous because the deal is not public.

(Reporting by Jessica Hall and Paritosh Bansal; editing by Gunna Dickson)