Skype, eBay's ( EBAY) Internet phone subsidiary, announced Monday Skype for SIP, a new version of its Internet calling software for corporate phone systems. SIP stands for Session Initiation Protocol, a leading voice over Internet protocol used by business telephony networks. Skype's SIP private branch exchange owners can benefit from Skype's low-cost calls to fixed phones and mobiles around the world, and can receive calls from Skype users directly into their PBX systems, the company said Monday. According to the Wall Street Journal, the new software is expected to allow employees to make domestic and international calls using regular office telephones, instead of a headset plugged into a personal computer. Initially, the company will charge about 2.1 cents a minute for calls to cellphones and fixed lines, but calls from computers to phone systems using the Skype software will be free, similar to what it now charges for its consumer service. Skype is known for allowing users to make free voice and video calls between computers, using voice over Internet protocol, or VOIP. Though the majority of users are consumers, Skype says about 35% of its customers already use the service for business purposes, the Journal says. Skype for SIP's beta program for business users opens Monday. The product will be fully launched later in 2009. The Journal reports Skype's announcement comes as eBay -- which bought Skype for $2.6 billion in cash and stock in 2005 -- faces pressure from investors to make more money from Skype or sell it.