need help with broken U740

Recently I accidentally slammed my phone into my car door and smashed the inside LCD screen. I cannot read text messages, but at least I could open them and call the person that was texting me. However, my inbox has just filled and I don't know the button combination to erase it. If anyone could give me a hand that would be great.

try this combination.
Left soft key, right soft key, the number 4, then "ok"

That should erace all your messages. if you want to just clear the inbox, replace the number 4 with the number 1