I too built a landline phone inspired by tincan. It runs off of an old macbook I repurposed as an ubuntu server, and routes through voip.ms. I used a pap2t linksys adapter so we could use a cool old analog phone. it mostly works, but for my youngish kid, its amazing and she loves it.

one nice thing about it is that i can set up call hours and a whitelist of allowed phone numbers, so she doesn't yet have to deal with strangers calling.