The Keyspan VP-24A may only work on 2.4GHz and not WiFi, but it's straightforward and relatively cheap, so you can buy one of these for your parents and not have to worry about whether their wireless router is set up correctly.
The phone weighs 92g with the battery, has a USB dongle to connect to your computer, a 15 hour battery life, and a 1200 hour standby life. It works just about the same as most other PC-based Skype phone, but costs only $79, which makes it pretty darn good in our book. Our book was also purchased on sale.
Product Page [Keyspan]
Keyspan VP-24A Cordless VOIP Phone Review [Slashgear]