What’s that special something in the air today? Is it spring? No, it’s Apple opening up the lines for pre-order of its recently unveiled iPad.

According to Apple’s Web site, devices ordered today will be delivered on April 3, which is also the date of general availability in the United States for Wi-Fi models. However, consumers will have to wait until late April for Wi-Fi + 3G models. Orders are limited to two iPads per customer.

Pricing is tiered according to which memory and wireless connectivity the customer desires. Currently, the iPad is available at $499 for 16GB, $599 for 32GB and $699 for 64GB. The Wi-Fi + 3G models, which are available in late April, will go for $629 for 16GB, $729 for 32GB and $829 for 64GB.

AT&T has signed on as the provider of 3G service for the iPad. Using new GSM micro SIMs for connectivty, AT&T will offer 3G users options of two plans, either 250MB of data a month for $14.99, or an unlimited plan for $29.99 a month. The 3G version, when combined with either of the AT&T plans, will include free access to all AT&T Wi-Fi hot spots.

As of 9 a.m. Central today, shares of Apple stock were up about a point from yesterday’s close of $225.