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Apple running out of some AT&T iPads

Select models of the iPad compatible with AT&T's 4G LTE network have seen their ship date moved back by three days.

The white AT&T version of the iPad is proving popular with customers. Josh Lowensohn/CNET

At least initially, AT&T is ahead of rival Verizon Wireless in the iPad race.

Select models of the AT&T variant of the iPad are seeing slight delays in their shipping dates, suggesting a shortage in supply. Specifically, the white version of the 16GB and 64GB AT&T iPad have seen their shipment dates pushed back to March 19, three days after the March 16 launch date.

All of Verizon's models will ship on March 16.

The 4G iPad is a source of bragging rights for the two carriers, who are jockeying for the claim to having the superior next-generation network. Verizon Wireless has a much wider deployment of LTE, the technology that Apple is touting, but AT&T has a wider deployment of a slightly slower--but still speedy--technology called HSPA+, which AT&T also calls 4G.

The early sales response provides a quick--if a bit premature--glimpse into which carrier customers are looking to stick with. AT&T has remarkably weathered Verizon Wireless and Sprint Nextel getting the iPhone, and in fact continues to sell the most iPhones. The carrier, of course, is helped by the availability of the 99-cent iPhone 3GS, alongside the iPhone 4 and iPhone 4S.

But with those looking for LTE, Verizon certainly has the advantage. Its network covers 196 cities and 122 major airports. In comparison, AT&T only has its LTE available in 28 cities. Still, that factor doesn't appear to be affecting sales, although it's unclear if consumers are aware that LTE for AT&T is still extremely limited (it is available in many major cities).

Some believe 4G LTE will finally prompt consumers to pick up a cellular-enabled iPad. For the most part, consumers have gravitated towards Wi-Fi-only versions. The customers who do end up with a 3G model rarely activate the connection.

One factor has been price. Apple released the data rates for the new iPad. It remains to be seen whether they are affordable enough for consumers.

Things may change this time around with 4G. The Wi-Fi-only models are all still available, regardless of memory or color.