if you think this you're not a regular iPod touch user. i've been carrying one in my pocket for 3 years. why? no monthly fee! Phone calls I don't make much, especially while i'm able to contact people via texts, email and FaceTime audio. I carry with me a cheap prepaid phone which maybe cost me $25 every 90 days.
So why don't you just get an unlocked iPhone (5 and 5c's can be found pretty cheap on eBay) and drop the cheap prepaid SIM card into it? No monthly fee there either.