After buying the Sony Xperia Miro, I couldn't get any APN for GiffGaff to save and the only visible APN was an 02 one. I did try and edit this but once you clicked save the APN was no longer visible and therefore unclickable.
It appears that on the new Xperia range that have the latest Android I.C.S will not give the owner an option to create a APN that saves. It will disappear as soon as you click the save option. The current TEXT settings wont work and nor do any apps, as the latest Android I.C.S will not allow any third party create or change an APN.
After many days trying I thought maybe trying to edit the current 02 APN, but in the past this didn't work either. So this time I did it this way and I have now had my phone running fine for a day and have no problems with Internet etc.
In the APN section, I choose the 02 Pay&GO (the only one showing, if you cant see it do a reset to default) so that it had the circle light with a blue light. I then enter it and edited it, now this has never worked any other time. But this time I left the name as
O2 Pay&Go and then edited the rest to...
MMSC: http:// mmsc.mediamessaging.co.uk:8002
MMS Proxy: 22.214.171.124
MMS Port: 8080
I hope this may help you. I did this on my phone on the 23rd September and have had no problems yet, I also bought the £10 goodybag and Internet etc is fine. I mention the Sony Tipo in the subject line as a few other members had the similar problem and I posted what I did on their threads, once they did it. They reported this worked.
I have posted this on here as a fellow member 'mrcool073' suggested I did to help others.