Using 3G on iPad2 in France

Nothing to do accountancy per se, but I am struggling to find the answer to this elsewhere so hoping someone can help.

I have an iPad 2 with a pay as you go data only SIM card from Three. So far as I can tell, to access the internet in non WiFi areas whilst on my impending French holiday, I can't use my normal monthly data allowance but I have to top up my account separately. I've done this, but is there anything else I have to do? The Three helpline seems to want my Three mobile number (I haven't got one) before I can speak to anyone. The support screens suggest I should be good to go now I've topped up my account, but I want to be sure before leaving if possible. Whilst my local High Street consists entirely of bookmakers, charity shops and mobile phone outlets, Three isn't amongst the latter so I can't pop in.