@nestort@quitter.no Users have these ways to automate mentioning:
1. AndStatus automatically creates one or all mentions if you reply to one or to all participants of a conversation.
2. When you want to add @user to a message that you are composing, you can switch to the Following timeline or to any timeline, where you can find a message of that user (you can also search for a message). As soon as you find a message of that user, long click on that message and select "Copy @author to clipboard" from a context menu and then paste it to the message that you are editing.

Regarding Following list in GNU Social. As I see, API allows me to see only those followed users, who are from the same GNU Social instance...