Had the same problem today. O2 guru told me to change max mms to 500000; it worked for me!!
Hope this helps
hi trust this way 1000 per cent it works great first download dropbox to your iphone take a picture you want to send open dropbox click on picture at top right of your screen you will see a sqaure box with arrow pointing up click that this will open screen with message facebook etc click message this will open new message put contact in who you want to send to click send thats it message sent i use this all the time you can now send to any phone you want hope this helps post if you do it to let me know how you get on