Incoming calls
If there are several contacts for one number saved in ACT! you can select one of the contacts by clicking on
to see a drop down with all available contacts. After you select a specific contact the contact detail will show up in ACT! (only if you set this option in the configuration!).Outgoing calls
If you dial by hand a number which is saved for several contacts you see a popup where all matching contacts are pre-selected.
If you want to create a history only for one contact you can remove the other contact(s).
If you let all pre-defined contacts in there the history will be saved for all shown contacts.