I'd suggest buying her a cheap phone and a month of phone service (after that, she'd have to pay), but she'd probably ring everyone's phones too loudly, LOL!

Is she familiar with this new service available? They're called "stores," and you go to them, pick out what you want, pay for everything, and take it home, and you get to keep it, and use it all for your very own! You should tell her about this! It's wonderful!