Just make sure you read the details... the sim card is free... but to use the "free" minutes and texts, you have to pay them a tenner a month ;-)
Correct me if I am wrong but I think you will find you have to spend £15 a month to get the free calls and texts, for £10 a month you will only get free phone calls.
Also the calls and texts are only free if you are sending or calling another Orange phone and there is no way of telling what network the phone is on by the number, if you sent or phone another network it will cost 10p for text and 35p/min phone call.
The sim card is free that is true but they will get £15 a month off you or you loose the free calls/text for that month (if you are one day late topping up you will loose the free calls/text for that whole following month).
This is how I read it, I may be wrong but they count on you getting it slightly wrong and spending money as a result so by all means get it for emergencies but be aware you must spend £15 a month every month to get the free calls/text.
And of course as there is no contract involved they can change the terms and conditions without notice, (and if they can they will at some time or other).
Take care and don't give one to the children as they will almost definetly get it wrong.