Adds an IM (instant messaging) address to the contact's list of IM addresses and increments its reference count.
Note that only one IM address per contact may be marked as "primary". Insertion and update operations (with insert_contact) will return an error if more than one IM address is marked as primary.
Duplicate IM addresses will not be added to the list.
| this | |
| im_address |
a GDIMAddress to add |