Sony Ericsson K510I

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

you can unlock it and switch over to another network , if you want to unlock, you can get codes here http://www.wickedunlock.com/sony-ericsson-k510i/rs11wp9/
you need to specify the country and network provider

I had this same problem. I only got the phone yesterday from Orange. I phoned them and updates didn't work so they're sending me a new handset. They said that sometimes there are items missing from the menus. You should phone Orange, I've always found them to be extremely pleasant and helpful. In fact, I'd rate them for the top customer care I've ever known.

When writing sms make sure you not scrolling to the bottom (the bottom line switches sms to mms.) Also in Settings-Messages check TEXT MESSAGES - and see options.

Hi,

I think the problem here is with your connection. I understand that you have the right settings from your operator...however you should check with them to see if your line is data enabled for MMS (this is how your pictures are sent....in an MMS message).

Try installing the software and then synchronising your phone with the software. then use the application to access your MMS/SMS.

hi

call the customer service of orange....they will set up message center number on your phone ...and send you sim updates ....and then you will get the text message options

cheers

Use this ;link to :

http://www.sonyericsson.com/cws/support/products/mms/k510i?cc=gb&lc=en

In your Menu/Messaging/Settings/Text Message/Service Centre make sure you have your Service provider's Message Centre number.
MMS are different settings.

Yes, you will need to send a text to your operator (O2, Orange, Vodafone, T-Mobile etc.) to get your MMS and other settings.
You should be able to obtain the number from the operator's website by searching for "Get Settings".