I'm on O2 in the UK, and my postpay net settings are the same as the mms settings, so I followed the guide and left fMMS using the postpay settings.

However, if I try to download the mms, it disconnects me from the postpay and then fails.
It's like it's trying to connect me to a different connection.
In fMMS config I have O2 Postpay GPRS as the access point, which is the correct name.

Any ideas?

It sees there's a mms waiting to be downloaded, so it's closer than the "General Error, speak to author" issues I was getting earlier!

Nicola