good afternoon DanReams
These two services have effectively merged over the years, and even Google's documents intermingle the documentation of the two.
Google Chat: This specifically refers to the Jabber protocol compatible text chat portion of the service, as near as I can tell. Thus, one can use Spark, PSI, Trillian, to use the service, or simply use the chat feature from within Gmail itself (which is what most people will do).
Google Talk: This adds the audio and video components.
Install it as either a browser plug-in or desktop software.
Plug-in - http://support.google.com/chat/bin/answer.py?hl=en&answer=159499 - PC & Mac - Offers video/audio chat within Gmail, iGoogle, and orkut
Desktop Software - http://www.google.com/talk/about.html - PC Only - Text and voice chatting, free multiple-user audio conferencing, file transfers, free PC-to-PC calls
Google Voice provides one phone number for all your phones, should you wish to have one. Two example scenarios of the utility of this feature are below.
[Note that phone number porting, of your cell phone or land line number, is available for a fee. I do not recommend this though, since you will then have to get a new phone number, for your cell phone, from your provider, to retain that device with a phone service. It is a useful feature for those of you who do not want to inform your contacts of your new or additional phone number. Personally, I just told people to use my Google Voice number instead of my cell number, and all was well. If they failed to do so, and continue to use my real, service provider given number, my cell phone still rings; the calls are simply not forwarded also to my other Google Voice devices. - d.r.]
When the Google Voice number is called, all of the devices that you define will ring. Whichever phone you pick up will be the phone you use for the call.
Thus, you will not need to manually forward phones from anywhere to anywhere else.
In my testing, I got the following results:
Answering the call on the PC:
Answering the call on the phone:
This does not address failure situations. I can transfer easily from PC to phone, via *, but pressing *, on the phone, will not transfer calls back to the PC. Nothing happens on the PC, and I'm using Chrome. Thus, the KB item does not specifically state what to do in such situations, although it does state calls could be picked up "from your desk", implying the feature is possible.
You can make outbound calls, from your Google Voice number, only from devices that have been enabled. Thus, you can use the PC, via Google Talk, easily. You could only use your cell phones or house phones, with that number, if you port your Google Voice number to those devices. If you do not port the number, your outbound calls from those devices will simply function as usual, originating from their usual phone numbers. See below Scenario #2.
If you do not wish to add cell phones and/or land lines to the mix, you can simply use your Google Voice number as an originating number when calling from your PC via Google Talk.
You can also use its voicemail feature, on your cell phone, and keep the "forward calls to…" turned off, for the cell phone. In this fashion you will easily be able to use Google Voice voicemail, and all its online features — also available on your phone — without having to give out your Google Voice phone number. See the below 'Voicemail' section for more details.
You can simply dial your Google Voice number — from any phone — press *, enter your PIN when the greeting starts playing, and access your messages. If you have a smart phone, you can download the Voice application, and even more easily access your messages.
You can have individualized voicemail greetings based on the caller's ID.
See http://support.google.com/voice/bin/answer.py?hl=en&answer=164648 for voicemail configuration information.
See http://goo.gl/hNNhb for information on how to choose your Google Voice phone number.
How Google Voice works: http://goo.gl/FkQwG
Google Voice is not a phone service but is compatible with phone services. For example, you can utilize it through a VoIP service (such as Google Talk), a cell phone, a land line, your work phone, etc. There is no software to install; the set up is all done via the Google Voice site.
Its voicemail is likely superior to your current voicemail.
You can define which devices ring based on who is calling.
I utilize these services as follows: