Embedded VOIP SIP Developers Kit 

Embedded Windows CE VOIP Developers Kit is your embedded telephony solution for developing software/hardware to enable device to device phone calls using SIP/H323 phone right at the electronics level.
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Express Talk VoIP Softphone 

Express Talk is software that works like a telephone to let you make calls from your PC. With Express Talk you can call anyone on the internet who has installed Express Talk (or any other SIP voip softphone). Calls are free.
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Phoner 

Phoner is a free softphone for ISDN and VoIP telephony. An answering machine and Text-To-Speech support complete the large package.
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