Thank you very much for your answers!
Now, just to make sure I've understood correctly, please let me know if what follows is correct:
1) As soon as I land to London, I find a T-Mobile store and I buy a PAYG sim with "Everyone" plan for 50p (I got the price from their online shop) and a 5pound top-up. I think there is no time for having a PAYG sim sent to hostel, because I'll be in London in less than five days.
2) I turn on the phone
then, according to the following link:
http://www.yourcallworld.com/payg/ca...?country=Italy
I call 07755 220 220, then I dial 0039 02 12345678 # and it places a call to an Italy landline for 3p/min (AND NOT 15+3=18p/min)
Is everything correct? I suppose that calling an Italy mobile would be more expensive (but on yourcall they don't write anything about mobile rates), but I think 3p/min to call a landline in Italy is really what I need!
Thanks again!
Ste