I have a samsung GT-E3210B phone and accidentally 'block by address' my friend instead of deleting an old text from her. How do I go about undoing this please?

SOURCE: i have accidentally block one

Just follow these steps
Menu>Settings>Applications>Message>General Settings>Block messages

Delete the contact in that list.

If you're not referring to this, go to Menu>Settings>Call>All Calls>Auto reject>Reject List

Then delete that contact in that list.

Hope this helps. <3

SOURCE: Delete old messages text & voice?

When first turned on, select "messages." then down arrow to inbox or outbox. Select choice. For outbox, down arrow to SENT. Select. Hit the center button. scroll down twice to delete the one message. Scroll down once more to delete ALL messages from the sent outbox. Confirm and out they go!

Now, does anybody know how to email text messages so they can be saved?

SOURCE: Can I retrieve deleted texts on LG Neon GT365?

It cannot be retrieved withouth opening the phone.

SOURCE: I have accidentally blocked a

Settings > Applications > Messages > General settings>Block Messages.
Delete the no you have blocked.

Testimonial: "A One!"

SOURCE: I HAVE A GT-S3650 SAMSUNG

Your wireless carrier can block certain numbers from sending you messages and/or phone calls.