Phantom Multimedia Message At regular, though infrequent, intervals I receive a multi media message in my inbox from 'δ@' which has no content. The message is completely blank. I do not have such a contact and I receive mmms so little that I'm sure it cannot actually be a real message from someone I know. 

I have a HTC Desire with Android 2.2 on Orange (UK).

What is this and what can I do about it?
You should be able to long-press on the text, and select View Message Details, this should give you the actual phone number it was sent from.

With this in hand you can go through your phone book and double-check that it's not anyone you know.

If it's not then you should be able to contact your service provider and ask them to block messages from that number. Also, many automated text services that use short message codes to send are set to remove you from their list if you reply with just the word STOP in a text message.