I'll go to great lengths to avoid social sign ups. I want nothing linked to those accounts. It mostly comes from distrust of app behavior. I don't want any app blasting anything to my entire contact lists. This might be an irrational concern but its real. I'll use Google account to sign up for any service BC I know Google won't let an app run wild w my contacts. Other services I am not so confident
"Several readers wanted to know how they could access the Other folder on their phones or tablets.
The answer: you can’t. The Facebook apps don’t permit you to see the Other folder. (You can, of course, go to www.facebook.com in your phone or tablet’s Web browser — don’t use the app — to work on the Other folder there.)"
You can on Android: hit the gear symbol next to the 'Messages' menu option in the Facebook app menu