Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Preme for Windows - Speeds up your window switching.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
GridMove - GridMove - A window management tool that can quickly arrange your windows into desktop grids.
Sipdroid - Free and open-source SIP/VoIP Client
WinDock - WinDock is a window manager ideal for large, or multi-monitor setups. Features: