Any advice, if I phone my sister's English mobile from my spanish mobile in Ibiza when she is in Greece, how does the costing work out. Does she have to pay half the call? Or would it be better if I used my English mobile, would that be cheaper?
who's her service provider in the UK? Texting would be cheaper. Depends entirely on which plan she's on, how much foreign received calls might be. OH is in Europe most of the time, we rarely speak, we text.
If you phone a UK mobile while it's in the UK it won't cost them anything.
You'll have to check if the roaming charges for your UK mobile are cheaper than the international charges for your Spanish mobile, but I suspect the Spanish one will be cheaper to make the call from.