First, get ALL your contacts into your People/Contact list on the phone.
Then, assuming you have a Google Gmail account, make sure you have the settings on your phone set to synchronize your phone's contacts with your Google contacts (online).
Login to your Gmail account and go to your contacts...there are buttons to select and combine multiple contacts into a single contact. Next time your Gmail contacts synch with your phone, they should be merged however you merged them.
There are a few other threads on this forum (and online) that go into this in more detail. The good news is that Gmail allows one to merge and combine contacts.
Of course, the Palm Pre and WebOS phones let you do this on the PHONE itself...frankly, that's one big advantage WebOS currently has over Android.