Phon Sim Cards

[secsee1]

I am off on holiday abroad soon and do not want to take my smart phone in case it gets lost or stolen so have decided to take an old sim unlocked mobile with me instead, but I need a free sim card that will allow me to top up as and when I need to and not on a regular monthly basis (as some cards require) as I will only want to use it for about 3 weeks, and of course it must allow calls to be made from abroad, I have looked but can only find sims that need a regular monthly top up any ideas with a link please.

[secsee1]

Thanks for your answer methyl, after watching BBC watchdog last week about people getting bills in excess of £5000 taking a smartphone abroad I decided to just take an old (tri band) mobile, I used to have an o2 sim that you just topped up as and when you needed to and the credit you had on it lasted from year to year but that sim got lost and o2 dont seem to do it again now,