Thank you ... i am useless with Phones but she did tell me to switch off my wi-fi so now i know why
wi-fi isn't the issue it is the data roaming that costs money. If the wifi is free, you can browse, send email, etc. normall just by being within range and choosing the network. If it's charagable, the first time you try to browse the internet, it will ask for credit card details or a pre-paid car number.
Roaming works like this: when you are in the UK, your mobile is tracked by your service provider, it knows where you are and this enables calls to reach you. When you go abroad, your phone finds the strongest signal and contacts the provider and checks to see whether your provider has an agreement with them, if it does, it tells your home provider it is tracking you and all calls are routed through to you. If it doesn't have an agreement, it will check the next strongest network until it finds one. If you move out of range of that supplier, it will try again to find a network. It may be better to scan and find a preferred supplier, then select that - your calls may be cheaper with France Telecom if you're on O2 UK for example. It changes all the time so best to check if there are any preferred suppliers.
The companies have merged a lot over the last few years but some old agreements pre-date these and a lot of them just charge a blanket rate regardless of which network you're on, even if it's their own.
Smart phones like the iPhone, blackberry etc. will connect and download emails but this is often at £2-£6 Mb, compare that to £5 or so for unlimited data at home. You really are best to turn off data roaming. One way is to change the values in the data settings by adding a letter e.g. Vodafone user id is web, change it to noweb then the settings are rejected and no roaming takes place.
another useful tip when roaming is to change all the numbers in your phone book by putting +44 instead of 0 - that means your calls will work in the UK and abroad.
If you're going to make a lot of calls, it might be worth buying an add on which will reduce the price of the calls or data. The O2 PAYG bolt-on is poor value, you'd need to make a lot of calls to justify the price of it.