I see a lot of replies already but might as well put our name out there as a viable solution for this setup.
With Yay.com you can download our built in house App that can be installed on your smartphone, and on your PC.
When you are in the office you can make and receive calls directly on your computer, and while you are there just put the App on Do Not Disturb (DND) on your smartphone and no calls will be sent that way.
Then, when you decide to leave the office, you can simply log off your desktop App, and you can disable DND on the smartphone App, this will make all incoming calls being taken there! So you will never miss a call when you are out and about. All that is required is that you have an internet connection, either by Wifi or your mobile data.
This is done at the touch of a button, so it should be relatively straight forward.
If you want more information visit our website www.yay.com