If you have two contacts that need to be merged together, here's how to combine them.
Select your two contacts in People
Click "Action" and choose "Merge selected profiles"
The first box shows your two contacts. Click "Next Step".
Choose which pieces of info you want for your merged contact. The third column shows what your merged contact will look like.
Click "Next Step".
Review your merged information.
Click "Merge Now"
Here are a couple of things to note about the merge:
Once you merge your contacts, the final contact will be in the groups that both original contacts were in.
The conversation history for these contacts will be combined into one conversation thread.