Yate is a next-generation telephony engine. While currently focused on Voice over Internet Protocol (VoIP) and PSTN, its power lies in its ability to be easily extended. It supports SIP, H.323, IAX, MGCP, Jingle, Jabber, E1, T1, analogic, robbed bit, ISDN PRI, BRI, and SS7. YateClient is an Instant Messenger and Voice application for Jabber/Jingle IM, SIP, H.323, and IAX VoIP protocols.
The Ozeki VoIP Service Checker is a tool you can use for checking the availability of VoIP services. It can be used to verify whether a given service exists, see whether it can be reached from a particular network, and check whether the user details (such as the username and password) to access the service are correct. It was developed because many mobile Internet providers block VoIP traffic.