Signal: You can only have one device, please use the migration tool to move from your "old" phone to your "new" phone. Also, upload all your contacts' details, we promise it's encrypted, and we don't see *anything* (except that we know all the phone numbers).
XMPP client: Please log in to your account. Here's all your stuff, same as on all your other devices.
Is there a reason it's not possible to view the "local" timeline of another #mastodon instance other than the one your account is on?
You can already view those posts in the Federated timeline, just mixed in with every other instance.