Why is my messaging on my Walkman Slider w580i messing up?

[treehugger:t]

I have a walkman w580i and its messing up.
I can recieve messages, but cant send any out.
they just stay in my outbox and dont ever send.
I can send voice messages but not text.
ive had these problems before and they just wont stop!
-whats wrongg?