When you ask for a mobile number to add a person for some mobile chat service don't forget about roaming. Some people - like me - use foreign mobile sim card because often they are better than regional. A number doesn't describe where the person is actually. I am Poles, I live in Poland and I use a Czech number. It is secure, it is cheap and much more confortable, because my network change provider to best signal and is not tied to one operator.

Sounds interesting, but what about roaming? You live in Polska, but the sim card thinks, you are in the Czech Republic.

Whole Europe have one tarif. When I call to Polish or Czech numer I pay the same amount, but when I am in T-mobile I can use just T-mobile BTS, when in Orange - just Orange network. If I use Czech numer in Poland my mobile change operator to the strongest signal without any additive charges.