Phone or Text a Friend
When viewing a User Profile or your list of Friends, you can phone, geocaching.com message, or text message them. The caching name must be in one of the Company, Nickname field of their contact entry in iOS for this feature to work. The name search is not case-sensitive and only looks for the caching name anywhere in the Contacts fields.
If you are looking at a log entry they made, you can tap their name/icon to go to their profile screen and call/message/text them as described above.