* Net loss 15 mln euros vs profit of 27 mln year-ago
* EBITDA down 3.7 pct at 279 mln euros
* Revenues drop 4 pct to 690 mln euros (Adds quotes, details)
LISBON, May 15 (Reuters) - Portugal Telecom (PT) swung to a net loss in the first quarter after a year-ago profit, hit by lower revenues, foreign exchange losses and extraordinary costs of its tie-up with Brazil's Oi.
PT's net loss totalled 15 million euros ($20.6 million) while a year ago it had a profit of 27 million euros. Revenues dropped almost 4 percent to 690 million euros, the company said, while earnings before interest, taxes, depreciation and amortization (EBITDA) dropped 3.7 percent to 279 million euros.
It said the revenue drop was due to a decline in the Portuguese telecommunications businesses, hit by pricing and high competition, and a lower contribution from international operations like Namibia's MTC, Angola's Unitel and Timor Telecom.
Still, it said its client numbers in Portugal grew in the quarter, including fixed, mobile and pay-TV services.
PT also said it had "financial expenses mainly related to certain banking services and other costs incurred in connection with ongoing business combination between PT and Oi", which affected the bottom line.
PT is in the process of combining assets with Brazil's wireless and fixed-line carrier Grupo Oi, in which it holds a large stake, to form a new company with more than 100 million subscribers. ($1 = 0.7294 euros) (Reporting By Andrei Khalip; Editing by Sophie Walker)