This app was mentioned in 2 comments, with an average of 1.00 upvote
> is calling my grandpa on her cell phone there
give simple smartphone with skype as a gift and use skype\viber. It would be cheaper then 50$.
For example, ukrainian carrier Lifecell for 1$\month give 500Mb 3g internet and unlimited data traffic for some messenger BiP, which can be used for audio\video calls.