Customers looking for an iPhone 3G may have to wait up to a month for Apple Inc. to boost its orders with suppliers and refill the pipeline, a Wall Street analyst said Thursday.

Meanwhile, current inventories continue to be tight at the company's retail stores, with just over a quarter of them having iPhones to sell Thursday.

"I bet we'll see these problems for another two to four weeks," said Gene Munster, analyst at Piper Jaffray & Co., referring to his estimate of the lead time necessary for Apple to increase orders from its suppliers and restock the depleted iPhone inventory. "Early demand has been more than they expected [because] they knocked it out of the park on the first weekend."

The iPhone 3G continues to be in short supply, according to Apple's own stock-checking tool, which it makes available to customers after 9 p.m. local time each day.

As of 1 a.m. EDT Thursday, 50 of Apple's 188 retail stores, or 27%, showed iPhone 3Gs available for sale. Wednesday, Computerworld checks found 48 stores, or 26% of the total in the U.S., claiming in-stock iPhones.

However, 13 stores said they had all three models of the iPhone 3G in stock: the 8GB version in black, and the 16GB version in both white and black. Wednesday, only nine stores had all three for sale.

The hardest-to-find iPhone 3G remained the US$299 black 16GB model, which is available Thursday in only 18 stores, or 9.6% of the outlets. Supplies of the $199 8GB iPhone 3G plummeted in the last 24 hours, according to Apple's inventory tool: 24 stores reported it as available Thursday (12.8% of the 188 in the U.S.) compared to 42 stores that said it was in stock Wednesday (22.3%).

Apple's $299 white 16GB iPhone 3G is available at more stores -- 46, or 24.5% of the total -- than either of the black models.

Munster echoed comments made yesterday by another analyst, Ezra Gottheil of Technology Business Research Inc., when he said Apple underestimated initial demand. And that's not how it played out last year. "There were outages last year, but not to this extent," Munster said, comparing the current situation with the launch last June of the first-generation iPhone. "This is a more sustained outage, and the demand seems to be sustained."

Last year, Munster said, there was an initial spike, but then demand tapered off, allowing Apple to replenish its inventory.

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