I recently bought a Sonyericson W300i which was on Orange. Unfortunately Orange is rubbish in my area so I have replaced the sim with my old vodafone one. I downloaded the WAP/MMS settings required from the sonyericson website, using vodafone as my service provider, and I have selected Vodafone WAP and MMS in the internet connections menu but it still won't work. I have wasted £1.00 today trying to contact vodafone customer service and keep getting cut off. The vodafone website doesn't have the W300i on their list of phones. So, if anyone has any ideas I would really appreciate it.
Just an update for reference in case anyone else has the same problem. I spoke to a Rep at SonyEricson and apparently even when changing the sim card the phone retains the Orange software. So, the WAP & MMS will never work, unless I put the Orange simcard back in! Even SonyEricson cannot download anything to the phone to correct it. Their suggestion was to take the phone back to Carphone Warehouse, as I made it clear when I bought the phone that I intended to replace the sim. They never told me I would have any problems. Oh well, you live and learn:-(