I think the reason you can not send of recieve MMS messages is because you don't have the settings input.

You can either phone up your operator and ask them to send it over

or

Visit Sony Ericsson's site, choose help and support and MMS messaging:
http://www.sonyericsson.com/cws/supp...0i?cc=us&lc=en
And input your phone and operator and it'll be sent over.