What phones are sold at full subsidy without a contract? I call BS on that. They might be subsidized but not the same extent.
You can't compare iPods and the iPhone. Completely different business model. The latter has to take into consideration the needs of the carrier (the iPhone was actually developed with AT&T, which means they have a degree of control over the product not seen in any other facet of Apple's line). Anyway, the point is that phones cost more without a subsidy (as provided on the bases of you agreeing to sign up for a contract).
It's really quite simple. You don't get a subsidy unless it involves a contract - and unless you can provide any proof of what you said above that's how it is 100% of the time. If the iPhone is sold without a contract it won't be subsidized to the same degree it is now (and it might even be full price). In either case it would cost more than it does now (to get the phone). Moreover, making a smaller iPhone would cost more in it self, because new technologies would have to be developed or employed, which only further disproves the likelihood of a "cheaper" iPhone nano. In the world of technology smaller always equals more expensive (at least initially).
Anyway, there won't be a nano or any iPhone update for a while (as is confirmed by the revelations surrounding Macworld).
For one thing you are way off target. Many phones are subsidized to the same extent as the iPhone and not all of them are smart phones. The Moto Razr was sold only 18 months ago with full $200 subsidy. All of the other smart phones are sold with the same subsidy as the iPhone.
Your comment about AT&T having input on iPhone is also completely off base. It's well publicized that in fact Apple told AT&T what they would be getting. This is obvious since the iPhone is the only phone that AT&T sells that isn't co-branded and doesn't have custom applications, etc, that tie the handset to their brand.
Apple basically told AT&T, "here's our iPhone, it will be the best selling phone ever, you will get lots of new subscribers, take it or leave it".
I don't believe for one minute that AT&T had anything to do with iPhone development beyond network/performance testing as the handset and firmware were being developed.
In any event, we will know if these rumors are true soon enough. I personally do expect a new form factor iPhone by July of 2009 at the latest, whether it be a nano iPhone, flip iPhone, iPhone clam shell, etc.