You're trying to get a named property. You need to use GetIDsFromNames to map the name of the property to the property tag you can use to retrieve the property. I would study this before proceeding:
http://msdn.microsoft.com/en-us/library/office/cc765864(v=office.15).aspx
Once you understand named properties, here's the Contact documentation that will tell you which named properties to fetch:
http://msdn.microsoft.com/en-us/library/ee178937(v=EXCHG.80).aspx
http://msdn.microsoft.com/en-us/library/office/cc765864(v=office.15).aspx
Once you understand named properties, here's the Contact documentation that will tell you which named properties to fetch:
http://msdn.microsoft.com/en-us/library/ee178937(v=EXCHG.80).aspx
