If skype is FREE why does my Iphone ask me my payment type?

I want to get skype because I'd love to see & talk with my grandchildren. I want to know why it says it's free, but yet when I go through attempting to download it I get a message asking me my payment type. I would also like to know if I'm going to be charged how much I'm going to be charged & how often? I'm really old, so please don't send me sarcastic messages. I need help with this. I just want to be able to do this without it turning it to a big fiasco. Again, why does it say it's FREE.

Its free… No extra charges… Its a free app… But the appstore wants your payment information to prove your over 18… Not to mention if you ever do want to get a paid app, then your info is already there… Its a security mesaure for the company and liability issue too… See terms of service for the exact verbage…

Google playstore, Apple Appstore, Windows Marketplace, and Blackberry world All have this policy

ONLY skype-to-skype calling is free
any calling skype-to-landline(or cell without skype) they charge a fee for, so they need a payment method.

if you use skype AND your grandchildren use skype, it will always be free.