This is a post I wrote a while back on Google Voice and VoiceChoice:
"Get a Google Voice number. It's just like getting a second line on the phone. The original cell number works same as always. Go into GV settings online and set GV to forward all calls to the cellphone number. Then no matter which number is called the phone rings normally.
For example, use the GV number for a business number and almost everything else. Only friends and family know the real cellphone number.
If you have postpaid cellphone service, you also have conditional call forwarding, which makes it possible for GV to handle all voicemail.
Install the GV app and you have visual voicemail for both numbers in one place. During setup choose GV for all voicemail service, NOT your service provider's voicemail. This activates conditional call forwardingi.
Remember, in initial setup outlined earlier, GV was setup to foward all calls to the GV number to the cell number. This is standard setup. Well, now unanswered calls to the cell number are forwarded by conditional call forwarding back to GV so GV can handle all voicemail, for either number, in one place and as visual voicemail.
To really make GV work seamlessly, especially if you've organized your contacts into groups, install Voice Choice 2.0.
It works like this: Setup VoiceChoice to, for example, call all Business Group contacts using the GV number and call all Friends & Family Group contacts with the real cell number. Set the GV app to make all calls through GV by default. But VoiceChoice 2.0 actually dials out. It automatically chooses to use either the cell number or GV number, depending on the contact group the contact being called is in. So, Business contacts see the GV (aka business) number, and Friends & Family contacts see the cell number.
This works perfectly. Routing is completely automatic. You don't have to do anything special or remember anything. Just use the phone normally and GV and Voice Choice 2.0 automatically deals with which phone number is used for outgoing calls.
With VoiceChoice 2.0 you can also choose which number is used for individual contacts instead of only by group. And GV wil do specialized voicemail messages by contact group and much more.
Note: There's a very good FAQ in the Help. Good setup explanation.
https://play.google.com/store/apps/details?id=com.google.android.apps.googlevoice
https://play.google.com/store/apps/details?id=com.voiceplus"