If the phone was made for TMO/Metro, you would need to root and find the splash screen.
The cellcos want their branded advertising.
That's why I buy unlocked. I use a TMO SIM and TMO doesn't even appear on the notification bar.
Straight Talk is owned by Trac Phone
If it's working with Straight Talk, ignore it. Metro was CDMA originally.
An app called iNotify took care of the problem