Facebook is testing SMS, multiple accounts in Messenger
It looks like the features are Android-only, at least for now.
Instagram confirms multiple account support is coming this week
Instagram multiple account support available to some iOS users
The long-awaited feature may finally be close at hand.
Instagram tests multiple account support on Android
Social media managers, rejoice!
Gmail's web app adds multiple accounts, mobile signature
I do have my Gmail account connected to my iPhone's Mail app through IMAP, but occasionally...