1.) Tap on any contact photo and the contact profile will open.
2.) Tap on Edit
From here you may edit existing information or add new contact details.
When adding new information make sure to tap the Add button in the upper right of the screen after you are done and then tap on the Save button on the next screen.
If you are editing existing information always make sure to tap the "change" button in the upper right of the window after you are done.
Then tap the Save button to save your changes.
Changing a phone number to make it mobile and enable the SMS icon.