Have you considered getting a T-Mobile phone with UMA? It's certainly not the cheapest option with standard mobile pricing of ~$30/mo and ~$5 of various taxes, but you have the added advantage of being able to have a "normal" phone when you're outside of Wi-Fi coverage.
If you're looking for the best value, you can get an Ipevo Wi-Fi Skype phone for ~$140 (a bit less than Netgear/Belkin; works fine). Add $3/mo unlimited US calling and $30 for SkypeIn so landlines can call you, and your total cost is $66/yr... That's tough to beat, and what I would do if I were you. The only downside is that the batteries for these devices may be a challenge to source, and as far as the phone, it's certainly no-frills.
The iPod Touch is not a solution I can recommend due to the lack of on-device microphone -- not to mention its battery on Wi-Fi being rather poor.
Good luck, and way to go on saving some cash!