A popular feature of newer phone systems is the ability to dial directly from Microsoft Outlook's Contact list. This is most often accomplished with a TAPI interface such as the open-source ASTAPI plug-in (http://www.voip-info.org/wiki/view/Asterisk+TAPI). This will provide the most basic calling ability from Outlook, but doesn't get a lot of updates and some people report having issues with it.
Note
TAPI
TAPI stands for Telephone Application Programming Interface and is simply a method for programmers to control telephones and telephone systems from a PC.
A newer product that has recently come out is 'Snap' (http://www.snapanumber.com), which takes dialling to a whole new level. Not only does Snap integrate with Outlook, but also it interfaces directly with our phone or SoftPhone to provide a complete call management and information system. Following is a very short list of the many features included in Snap: