For many people the internet and digital technology is changing almost every aspect of their life. Buying things online is becoming increasingly popular, MP3s are replacing CDs, digital photos are replacing film, Personal Digital Assistants are often used instead of a pen(!), you can watch videos and movies in your browser, research is helped with online libraries and sites like wikipedia, laptops are becoming entertainment appliances, many people do all of their banking online...the list goes on.
That means many industries are also being transformed. One industry which is, at this moment, going through a bit of a crisis through recent technological developments is the telecommunications industry. Previously controlled by monolithic 'telco' companies and corporations, the telecommunications industry is being challenged by a group of technologies which fall under the rather broad heading 'Voice over IP' (VOIP).
VOIP means using the internet to make phone calls. Either computer to computer calls, or computer to phone calls. There are many popular softwares that enable this, the most well known being Skype. However this field is very diverse and there are many many softwares that enable this kind of calling. Softwares which enable VOIP from your computer are called softphones. Softphones are used to make computer to computer calls, computer to phone calls, or make conference calls. Skype is a softphone and so is Linphone (there are many others).
However before you get too excited, you should know that you can't use just any softphone to call any other softphone. Skype, for example, only works calling telephones or other Skype software. You cannot use Linphone to call someone using Skype and you can't use Skype to call someone using Linphone. It is possible for Linphone to call some other types of softphones, but you need to know who you are trying to call first and find out what software they are using and how it is configured.
If you are lucky their softphone will be using a way to call known as the SIP protocol. This type of softphone is known as a sipphone. You can see things are already gone a little geeky and you haven't even tried to make a call yet.
Knowing who you can and can't call, and how, is the key to using VOIP software, and it can get tricky.
To cut a long story short, if you aren't already familiar with this area you may need a little real life geek help. Thats sometimes the way with emerging industries and technologies.
Linphone has a version with a Graphical User Interface (GUI) and a command line version called Linphonec. Both versions run on Linux and the command line version also works on many Personal Digital Assistants and mini computers (such as Gumstix http://www.gumstix.com).