It's taken me a few days to figure out how to explain this, but after using GrandCentral for about a week I think you may find that this is a must-have app.
GrandCentral is a service that offers you a normal, but special, phone number in the area code of your choice. You can then link all of your other phones to this number. When someone calls your GrandCentral number all of your linked phones ring (depending on how you set it up, see pic below). It also creates a unified voice mail system which can be accessed over any of your phones or through a web interface.
This has come in very handy recently as we've been moving around in preparation for returning to the country in which we work. First I set up GC to ring my home number and my cell phone. Then when people called my GC number both phones rang and I was able to pick up either one. Over the last several days we've been moving into my mom's house for a few weeks before flying out of the country. When we made the move to "mom's", I added her number to my GC profile. Now when my friends call MY SAME NUMBER, my home phone, my mom's phone and my cell phone ring.
Yesterday one of the pastors from our church wanted to return a call I put in to him. He had no idea where I was. I might have been in our old house packing. I might have been on the road or even at my mom's. But it didn't matter because he called my GC number; GC makes it irrelevant. His comment after I explained the service to him? "Man, this is the phone I've always wanted...isn't this what everyone wants?" Okay, okay, I see you waving your hand, "Ya, but
he could have just called your cell phone, which you always have with you!" Yes, that's true. But first, I don't always want to talk on my cell phone and two, GC also handles all my voice mail. I don't have to check my cell phone's voice mail and my home phone's voice mail, etc.
The idea behind GrandCentral who's motto is, "one phone number for life." Right now GC doesn't handle international calls, but they claim they may add that in the future. I could, however, connect GC to a SkypeIn number and truly have one phone number for life. You can read more here, here