Help MMS problems Xperia x8

[feanor]

I havent any credit, but do have a wifi net connection. I've asked people to message me with images a fair few times and everytime the image comes its a little box saying 'message not downloaded.'
I hold down on it and hit 'download message' but nothing happens, or it says 'message cannot be downloaded'. Is this just because I dont have credit and it insists using the networks internet or is it a problem with my phone?

 

[coman_nick]

Talk to your service provider to enable MMS send/recieve and ask them how to set up your phone.