Readers doing their own surveys reported stores running out in Michigan, New Jersey, Pennsylvania and Texas.

Piper Jaffray analyst Gene Munster called 20 Apple stores across the county on Wednesday and found no iPhones anywhere. Zero.

Even AT&T seems to be running out of inventory.

It’s a mismatch of supply and demand not seen since the summer of ’07, when Apple (AAPL) offered would-be buyers state-by-state listings — updated daily with little green and red lights — showing which stores had the devices in stock.

What’s going on? Piper Jaffray analyst Munster puts odds on the possibilities:

• 20% chance Apple is dealing with some kind of production or manufacturing problem.

• 80% chance that Apple is clearing inventory and has a new version of the iPhone coming earlier than anticipated

Meanwhile, if you’re looking for an iPhone, Apple.com is still promising to ship within 5 to 7 business days. And a search on eBay on Wednesday afternoon turned up 2,346 listings for iPhones and iPhone unlocking services.

UPDATE: Bernstein Research’s Toni Sacconaghi weighed in on the shortage  in a report to clients. He notes that while iPhones seem to be out of stock at virtually all Apple retail stores, they are widely available at AT&T outlets in the U.S. and at O2, Carphone Warehouse, Orange and T-Mobile outlets in Europe.

This suggests to him that rather than clearing inventory for early release of a new iPhone, Apple is probably dealing with a production-caused shortfall with a “family hold back” strategy. Rather than upset its partners and reduce the number of iPhones it could report as sold in the March quarter, Apple supplied its partners before it supplied its own stores.

A prolonged shortfall, he estimates, could lead to lost sales of 20,000 to 40,000 units a week.