MANILA, Philippines -- The Philippines remains strong in outsourced voice-based services but needs to have adequate supply of skilled workers to sustain its growth, according to an outsourcing advisory firm Tholons.

In its report, Tholons included the Philippines among the offshore "centers of excellence" in Asia Pacific alongside India and China.

Tholons was referring to countries that have built domain expertise in certain BPO (business process outsourcing) areas. The Philippines, for one, is recognized in the area of contact center services or call centers.

Tholons, which has offices in India, North America and Europe, estimates that 40 percent of the total BPO business in the Philippines comes from voice-based services.

"The Philippines leads in voice capability even though the market scale is small," the report said.

By Tholons' definition, offshore outsourcing is roughly divided into IT outsourcing and BPO. The latter includes call centers and back-office processes such as HR (human resources) and finance and accounting.

Asia Pacific remains the number one destination for outsourcing, largely due to India. Canada, meanwhile, is the second largest destination for BPO.

As of 2006, the overall offshore BPO market is valued at $25.6 billion while the overall offshore IT market is at $36 billion and growing. The combined market is growing at least 20 percent every year, according to Tholons.

The emergence of China as a viable destination, meanwhile, promises increased "flow" of outsourcing contracts to Asia Pacific, Tholons said.

The report also noted that clients are more open to experimenting with multiple offshore models now than three years ago, which indicates maturity and growing client confidence.

Key functions will get concentrated in these centers of excellence but would work seamlessly. Tholons sees India and the Philippines as "best of breed" service providers in areas like HR.