My first thought after reading about placing a telephone call directly from my PC was... cool!
PC VoIP is basically using a software application, your PC headset (microphone and speaker) and your VoIP provider service to place an outgoing phone call.
Here's a snapshot of the Vonage Softphone VoIP service:
There are several different forms of PC VoIP... I'll talk about a few you may consider.
Vonage offers a package called "SoftPhone". You download the application, make a few setting choices and you're up and running to make - or receive - phone calls. That's right, SoftPhone lets you make and receive calls directly from your PC with a dedicated phone number assigned to you. BTW, you can choose the location of the phone number... local or nationwide. It's only available with an existing Vonage account for $9.99 a month, $0.039 per minute (at this writing) and comes with 500 free minutes. One note, the 911 service available with all other Vonage plans is not available with SoftPhone. Call quality is excellent and comparable to other Vonage plans and standard phone lines. Vonage has been rated a "Best Buy" at PCWorld, received an "Editor's Choice" from CNet and received the LapTop Magazine's Editor's Choice award.
Net2Phone has a service called CommCenter. It adds fax, PC to PC and instant messaging to the outgoing phone service, but lacks the ability to receive incoming calls. You don't have to have an existing account to sign up, you can setup an account just for the CommCenter service and you are not assigned a phone number. To use the service you download the software, open a free account, load funds into your account and you're ready to go. PC to PC calls (calls to other Net2Phone CommCenter users) are free, all other calls and fax rates are based on the location of the call. For example, calls to the US are currently $0.02 per minute.
Lingo doesn't currently have a PC VoIP option.
Skype has PC VoIP package called "SkypeOut". The Skype service is basically a P2P (peer to peer) software application where you can connect with other Skype users at no cost. The "SkypeOut" service is an extension of the software that allows you to place calls to just about anywhere for about $0.02 US a minute (as of this writing). You load your account with a minimum of 10 EUR (about $13 US) and all calls are deducted from your balance. The sound quality is excellent, sometimes like a cell phone, but most often as good or better than a standard phone line.
Bottom line: If you're looking for a solid service with a permanent phone number that you can make and receive calls, Vonage is your choice. If your needs demand fax, chat, and outgoing calls only, Net2Phone has it. If you want to connect with others via a P2P network along with phone conference, chatting, file transfer and the option of calling anywhere (for about $0.02 per min), check out the popular Skype service.