* Q4 net profit 9.12 bln baht vs 9.48 bln forecast
* Aims for 2015 revenue growth of 3-4 pct vs 1.2 pct in 2014
* Q4 voice revenue down 15 pct, non-voice up 41 pct (Adds comments on outlook, details)
BANGKOK, Feb 5 (Reuters) - Advanced Info Service PCL (AIS) , Thailand's largest mobile operator, reported a rise in fourth-quarter net profit below market expectations on Thursday as falling voice revenue partly offset improved mobile data usage and lower costs.
The company, 23-percent-owned by Singapore Telecommunications Ltd, posted a 3.5 percent rise in net profit to 9.12 billion baht ($280 million) for the October-December quarter, lower than the 9.48 billion baht average forecast by seven analysts polled by Reuters.
Fourth-quarter revenue from voice service dropped 15 percent year on year, while non-voice revenue jumped 41 percent.
Hit by falling voice revenue amid weak domestic consumption after months of political unrest last year, AIS has changed its strategy to become an integrated telecoms service provider by offering mobile, fixed broadband and digital content services.
Revenue should grow by 3-4 percent this year with strong demand for mobile data, versus 1.2 percent last year, the company said in a statement.
For 2014, net profit was down 0.7 percent to 36.03 billion baht while service revenue rose 1.2 percent.
AIS plans to invest 40 billion baht this year to expand capacity and roll out fibre optic to support both mobile and fixed broadband businesses.
Thailand's second-largest listed company aims to acquire 80,000 fixed broadband subscribers in the first year of operation, it said.
AIS shares, valued at $22.5 billion on the Thai bourse, closed up 0.4 percent on Thursday before the earnings announcement. The stock hit a 15-month high of 257 baht in January. ($1 = 32.6200 Thai Baht) (Reporting by Khettiya Jittapong; editing by Vincent Baby)