Phone Dialer for Apple Watch adds a full featured number dialer to the Apple Watch.

This helps people dial numbers that aren't in their contacts. This app comes with a simple and extremely recognizable interface, and support for saving contacts.

When you dial a number you can initiate a call with the number, and after you dial the number, the app will provide you options for saving a contact, and the contacts will seamless be added using the phone number you just dialed.

Credit:
Arjeet Tipirneni for the Contacts Saving Feature