* Q3 profit jumps as costs fall, user base grows

* EBITDA margins jump; market share rises

* ARPU falls 10 pct from yr-ago, but rises vs Q2

* Shares jump as much as 6.3 pct from Wednesday close (Recasts to add byline, remarks from CEO Lima interview)

By Cesar Bianconi and Guillermo Parra-Bernal

SAO PAULO, Nov 5 (Reuters) - Vivo Participacoes, Brazil's largest mobile phone carrier, said on Thursday that third-quarter net income more than doubled as operating costs and financial expenses dropped and data services revenue swelled.

Sao Paulo-based Vivo, a joint venture owned by Portugal Telecom (PTC.LS: Quote, Profile, Research) and Spain's Telefonica (TEF.MC: Quote, Profile, Research), reported profit of 340 million reais ($196 million), up from 133.9 million reais a year earlier, according to a securities filing.

Vivo's (VIVO4.SA: Quote, Profile, Research)(VIV.N: Quote, Profile, Research) cost of goods sold, such as mobile phone equipment, fell for the second straight quarter. Costs and operational expenses declined 1.2 percent year-to-year, while provisions for unpaid bills dropped 58 percent.

"Vivo showed good cost control, and it is worth highlighting that selling expenses fell 1 percent quarter-on-quarter despite nearly doubling net additions" in the same period, said Barclays Capital analyst Michael Morin.