Share your experience!
when you say full backup do you mean repair it with either PCC or SUS?
Update Service (SUS)
http://www.sonymobile.com/gb/tools/update-service/
http://www-support-downloads.sonymobile.com/Software%20Downloads/Update_Service_Setup-2.11.12.5.exe
Bridge (for Mac)
Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
Don't forget the Kudos
I wonder if you have a faulty screen, test it with this
https://play.google.com/store/apps/details?id=com.sonymobile.androidapp.functiontester
Are you sure its not because you are touching the edge of the screen with other fingers? I've read another thread and the user complained about the screen being too sensitive and this created similar issues.
Contacts
open the phonebook > menu > filter > perhaps some contacts were stored somewhere else, I suggest that you back them up with Google
Could you elaborate on the ear speaker? Because if the problem persists after repairing the phone it might be a hardware issue.
Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
Don't forget the Kudos