I cant send a song as an MMS on my Sony Ericsson W580i cell phone.. how do i do it ??

i cant open my mms messages or send them how do i fix it

The signature works differently ,type the message and in the advanced options use the add signature to insert your signature.By adding your signature message will be send as picture message ie mms message not as text message.
You can find useful information at the following link
http://forums.wireless.att.com/t5/Sony-Ericsson/New-w580i-owner-with-some-questions/td-p/1555891

the song needs to be removed from the play list directly if it only pops up in the media player. just go on playlist edit play list and remove the song.

Friend, MMS is a paid service and has to be activated by the service provider. Get in touch with their helpline and get it activated and also ask them for the MMS settings. These settings are also specific to the service provider and hence only they can provide them.

did at any point the phone got wet and if not its maybe a deffective phone tell the cell phene provider and they should send you the exact same phone for free

u cant get a phone lock

before receiving or sending picture messagers u must activate the MMS settings by requesting ur network provider only then u can send or receive picture msg 
if u hav a signal problem nothing can be done
a small suggetion is in stores they sell a external antenna try getting it and fix it 
tat helps in signal problem

Well, the MMS Service can be activated on your phone by simply visiting the Home website(Sony) with the following website address:
"http://www.sonyericsson.com/cws/support/phones/detailed/phonesetup" and clicking the option that says MMS settings..
   After which, you'l be asked for your Location and the Network Operator followed by certain other simple phone-related questions to have the MMS settings to your phone via SMS...
There, that'l solve your problem. 

call u'r network provider and and they will give you the configuration and proper guide to set ur gprs..it's because somehow other phones on their network are not supported

what kind of sim card are you using in it now? in order to receive send pictures (other than bluetooth) you need a sim card. and if you have an att sim card in it and it is not letting you send receive picture mail, your internet is off. (we call this WAP in the industry). The easy fix:

Call ATT if you are using it on the ATT network and tell them to have the internet pay per use turned on. Then you will be able to receive MMS messages.