My personal take on this is that I'd keep paying the $50. Are there cheaper options? Sure, but is it worth the stress of taking away something from someone who is now in their twilight years? That depends on your/their financial situation.

Google Voice is free, and if you're a younger person on a tight budget I could see you going this way. But an elderly person? No shot. The furthest I'd reach would be to go to a mobile phone on a Mint Mobile plan. Mint Mobile will run you $15/month, but you'll end up paying full price for a phone.