One of the things I planned to do with my new cell phone number is use the Google Voice app to re-direct all my calls through it.  That way all callers would see calls coming from that number and I would receive calls through Google voice.   There are several advantages to doing so:

• Google Voice allows me to have multiple phones it rings, depending on where I am and when.  I can set this up by schedule or manual.
• I get a great voice mail app by using it.  Google Voice actually tries to transcribe the call so I can see what the jist was by looking in the app or online.
• I can route people specifically to voice mail and flag callers as spam callers
• I get a number that I picked

A wrench manifest in the works though because T-Mobile has a feature called "My Faves" and it allows you to have 5 numbers that you can call free of minutes.  Additionally, calls that are T-Mobile to T-Mobile are free.  But I loose that benefit if I use Google Voice for any of those calls.  The obvious way around this conundrum is to set up Google Voice as one of my five favorites, but this seems to be expressly forbidden under the terms of service, and seems to be a bit of a dishonest rip-off kind of thing to do.  I'm not even sure they don't have a way of stopping you from doing it.

So, what I'll probably do is use Google Voice when people need my phone number but I don't want them to have my cell number.  That way I keep control for those calls.  I'll just send them all to voice mail.