I use my iPod touch as a communications device all the time. While it's not very effective as a phone due to the speaker placement (although I do use it for that on occasion) it makes a great text messaging device. But of course, I'm constrained by Wi-Fi. So I only use it around the house.
But add 3G and suddenly it's practical to use anywhere. Suddenly, it's a phone, minus the onerous voice plan.
I don't have a land line, so my mobile phone is my primary communications device. Yet over the past several years I've used fewer and fewer minutes in my account. That's largely because I now make so many calls using VoIP, either on my mobile phone, or my computer. I even use my iPad to make calls on occasion (and to send SMS messages all the time). It's weird-looking, and kind of ridiculous, but it works and it's come in handy more than once.
Despite that, I'm still paying AT&T about $US100 a month for the voice and data plan on my mobile phone. Meanwhile, I pay about $US30 a month for the data plan on my iPad. If I could use a similar plan on my iPod, it would be a huge cost savings to me over the course of the year. More than enough to justify buying a new iPod touch.
If Apple relocates the speaker on the iPod touch to align with my ear, and adds 3G support that let me pick a data plan from a variety of carriers, I'm kissing my mobile phone service goodbye forever. It would be a gut punch to carriers, but it would be a massive boon for consumers. And it would make the iPod Touch every bit as revolutionary a device as the original iPhone.
So while, yes, I'm sceptical, I'm also very, very hopeful. Bring it.