I’d suggest using: www.voipdiscount.com
I’ve been using this VoIP program for years. You can call someone on their landline phones (in approx. 45 countries) nearly for free. It costs €10 for 120 days!
Considering the fact, that you can speak unlimited it’s close to free, in contrast to
SkypeOut where you pay pro minute (out of Pro).
Tutors can use this program if somebody has computer or online challenge.
I guess somebody is using this (or similar) program either. e.g www.peterzahlt.de or others.