Have you checked that you got the internet settings correct on the phone? The internet connection can be very slow if the settings are even a little bit incorrect.
Also you said data roaming is on - that's good as data roaming is needed for the data connection to work with 48.
Have you checked your settings from here? There's a link to configure them using the automated service (at the top of the thread) and below instructions if you need to configure the settings manually in case the configurator doesn't work for your phone.
Did this help any or is it still very slow?
