Hi, I have 10 years experience in software design and development, experience in C++,C# 2.0/3.5/4.0 and web applications
(Javascript, CSS, HTML, Asp.Net, SOAP, AJAX, IIS 6.0/7.0/7.5), MS Sql 2000/2005/2008.
First of all I will not say that "I can do it for you".
I wll say that I can implement Windows phone application, that will work for windows phones, so with this application you can ping your friends that have also windows phone application installed. If you add some of your friend, then you can ping that friend and see his gps location.
Of course there will also web application, so you can from your laptop also have "ping" funcionality. Of course you will have username and password for this application.
Once again, I can implement windows phone application with this functionality.
Best regards