I am now looking for voip solutions. And found information about Voip sdk.
According to their website Voip Sip SDK - The easiest way to add dial and receive phone calls features to your applications. Soft phone sdk to make your soft developing easier! SIP activeX, activeX voip sdk


Voip sdk is based on IETF standards (SIP, STUN, etc.), so it should be compatible with other standard based products such as Asterisk, OpenSER other.

They have all features I need:
# Dynamically loadable codecs
# Registrar support
# Play wav files into conversation
# Record conversation into file
# Hold/Retrieve call
# Forward Call (Blind Call Transfer)
# Transfer Call (Attended Transfer)
# Mute Sound
# VPN support
# Noise reduction
# Auto gain
# Jitter buffer parameters
# Samples on Delphi, C#, VB, VB.NET, C++ 2005, C++ 6.0, HTML (SIP ActiveX)
# Windowless samples on C++ and .NET
# DTMF
# Adaptive silence detection
# Adaptive jitter buffer
# STUN support
# Comes as ActiveX control

But before I will download the evaluation version I would like to hear other people experience.