* Zon, Sonaecom mobile unit merging to be Portugal No.2
* Zon already present in Angola, Mozambique
* Zon shares jump 6.6 pct, Sonaecom up 3.5 pct
* Synergies seen in top half of 250-700 mln euros range (Updates with Sonaecom CEO, Zon negotiator)
By Filipe Alves
LISBON, Dec 17 A merger between Portugal's Zon Multimedia and Sonaecom's mobile unit should help the enlarged company expand abroad and reduce its dependence on a recession-hit home market, a Zon official said on Monday.
Sonaecom and Zon said on Friday they were negotiating a merger to create Portugal's second-largest telecoms firm, aiming to better compete with former monopoly Portugal Telecom .
A merger between Zon and Sonaecom's mobile unit Optimus had long been expected by investors and was initiated by Angolan investor Isabel dos Santos, who increased her stake in Zon to almost 30 percent in June.
Mario Leite Silva, who is leading Dos Santos' negotiations on the deal, said the merger would pave the way for an international expansion strategy for the new company.
"If the merger goes ahead it could lead to a deepening of the multinational strategy, extending it to other regions, which would allow the new company to be present, simultaneously, in complementary markets," Leite Silva, a Zon board member, told Reuters.
Leite Silva gave no further details but Zon is already active in Angola and Mozambique through a 30 percent holding in Zap, the fast-growing pay-TV business launched three years by Dos Santos in Angola. Dos Santos is separately the biggest shareholder in Angolan mobile phone company Unitel.
Shares in Zon Multimedia rose sharply on Monday in response to the merger plan. Zon shares were up 6.6 percent at 3.0 euros by 1420 GMT, having hit their highest since mid 2011, while Sonaecom shares also reacted positively, up 3.5 percent.
The chief executive of Sonaecom, Angelo Pauperio, said his company's board backed the merger plan, including France Telecom , which has a 20 percent holding in Sonaecom.
"This operation was approved without reservations by Sonaecom's board, where there are representatives from Sonae and France Telecom," Pauperio told a conference call. "Everybody gave enthusiastic support."
Conglomerate Sonae is controlled by Belmiro Azevedo, one of Portugal's richest men, and has a majority stake of 53 percent in Sonaecom.
Analysts at UBS estimated synergies from the deal could exceed 700 million euros and said they expected the proposal to win shareholder support.
"We believe the deal is likely to find ... approval given that positive operating impact, as well as relevant influence of Isabel dos Santos on key shareholders of Zon such as BPI," UBS said, referring to Banco BPI, Portugal's third-largest listed bank which holds 7.55 percent of Zon.
Pauperio said analysts have estimated synergies from the merger of between 250 million euros and 700 million euros.
"I think, in an operation of this kind, we should expect synergies in the upper half of analysts' estimates rather than in the lower half," he said, adding that a detailed study of the synergies will be carried out.
Dos Santos, who also owns 19.5 of BPI, is the daughter of Angola's president and has been snapping up assets in Portugal in recent years, taking advantage of cheap prices during the country's debt crisis.
Zon is the largest pay-TV firm in Portugal and fourth-largest telecoms operator in terms of revenue. Optimus ranks as Portugal's third telecom firm after the local unit of Vodafone Group Plc.
A merger could help the companies during tough economic times in Portugal, where the economy has entered its worst downturn since the 1970s.
"We believe the merger makes strategic sense, especially given the tough macro-economic backdrop," Nomura said in a research note.
Shares in Portugal Telecom were down 1.6 percent at 3.764 euros while the general Lisbon market was flat. (Additional Reporting by Sergio Goncalves; Writing by Axel Bugge; Editing by Hans-Juergen Peters and Mark Potter)