I want to share a best IP phone toolkit that called IP Phone SDK. It provides a powerful and highly customizable solution to quickly add SIP based dial and receive phone calls features in any software application. It accelerates the development of SIP compliant soft phone with a fully-customizable user interface and brand name. It contains a high performance VoIP conferencing client capable of delivering crystal clear sound even for both low and high-bandwidth users and SIP compatible devices (hardware and software). It enables a worldwide communication over the internet or intranet networks delivering superior voice quality and supports DTMF, adaptive silence detection, adaptive jitter buffer! It is based on IETF standards (SIP, STUN, etc.), so it should be compatible with other standard based products such as Asterisk, GNU Gatekeeper other.
To find out more about this tool please check their web site URL="http://ipphonesdk.com/"
. You should try this toll because a free trial available on their web site. I hope you will like this tool.