I have a few numbers stored in my phone already prefixed with '141' (to withhold my number) and earlier while trying to call one I was getting the message 'sorry, this service is currently unavailable' or words to that effect.

I couldn't work out what was happening but I think I've worked it out.

If you use the 141 service on a T-Mobile handset, but while connected to Orange, it doesn't allow you to connect the call. It may well be the case vice-versa.

Is it just me and my phone, or has anyone else noticed this?

I wish I never joined the tmobile/orange share signal service as now when I do lose a tmobile connection and switch to an orange signal I can no longer use internet as my handset says im roaming.

Try #31# instead of 141. That's the GSM standard code.

*31# is the same as 1470 (to reveal your number) incidentally....

Turn your data roaming on then?!?!?

Yup, nice and easy isn't it - my Android told me about roaming charges first time I used data on T-Mobile, just disabled the message and continued on fine

Yup its really easy to turn on data roaming and that will enable data on the network you are roaming on.

With no charges?

With no charges.

Just make sure if you take the phone abroad and DON'T want to use data that you turn it back off.