You can quickly add the sender of any message you receive to your My Contacts list, allowing you to communicate with that contact more easily in the future, and to add further details to their contact record e.g. their telephone number.
To add the sender of a message as a contact:
In the Inbox or an open message, position the mouse over the name of the person you wish to add to your contact list
From the contact card displayed, click on the Add to Contacts button in the top-right corner of the contact card
The sender of the message will be added to My Contacts in your contact list.