* Q3 REBITDA 86 mln euros vs 75.3 mln expected
* Says 2015 REBITDA to top 260-280 mln euro guidance
* Average revenue per customer 23.9 euros from 23.5 in Q3 2014 (Adds CFO comments on Belgian market)
BRUSSELS, Oct 20 (Reuters) - Belgian mobile phone operator Mobistar on Tuesday said it would beat its 2015 guidance, after a solid third quarter driven by higher spending per customer.
Recurring core profit (REBITDA) unexpectedly rose 11.3 percent in the third quarter to 86 million euros ($97.4 million), well above the 75.3 million expected in a Reuters poll of five analysts.
Mobistar added it would exceed the high end of its 2015 guidance for REBITDA of between 260 and 280 million euros.
The group said average spending per user increased to 23.90 euros in the third quarter, compared to 23.50 euros a year ago, as a faster fourth generation (4G) network enticed customers to use more data.
"Their usage is significantly higher than even the same customer when they were still on 3G," said Chief Financial Officer Ludovic Pech, adding this allowed the company to sell higher-priced monthly subscriptions.
The Belgian telephony market was shaken up in 2012 when a new law limited lock-up periods for customer contracts to six months, causing companies to launch promotions to nab each other's customers. Compared to the third quarter of 2012, Mobistar's core profit is down by some 30 percent.
Pech said he believed the market had become more stable but warned that in the fourth quarter, which includes the Christmas period, competition was typically toughest. ($1 = 0.8827 euros) (Reporting by Robert-Jan Bartunek; Editing by Shri Navaratnam and Philip Blenkinsop)