Apple released a version of its iPad tablet computer over the weekend that features 3G cellular connectivity, and the device may be an even bigger hit than its Wi-Fi only cousin, based on early sales reports.

Piper Jaffray analyst Gene Munster said that he believes Apple sold about 300,000 iPad 3G units over the past three days, bringing total iPad sales to more than a million.

Meanwhile, there's other signs that it could be tough for consumers to get their hands on an iPad 3G, at least for the next week or so.

Apple's online store is reporting a waiting time of five to seven days to fulfill new orders for an iPad 3G, as well as Wi-Fi only iPads. For its part, electronics retailer Best Buy is only selling the units in select stores, "in limited quantities, no rainchecks," according to a note on its Web site.

Best Buy is not selling iPads over the Internet.

Not surprisingly, the shortage of iPads—particularly the 3G units—is leading to price gouging on eBay. As of early Monday, numerous sellers were hawking the device at prices several hundred dollars higher than their official retail price.

Official pricing for the Wi-Fi only version, which features 802.11 connectivity, starts at $499 for the 16GB model, $599 for the 32GB model, and $699 for the 64GB version.

The Wi-Fi + 3G versions are priced somewhat higher. The 16GB model is $629, the 32GB model is $729, and the 64GB version is $829.

Apple shares were up .87%, to $263.35, in pre-market trading Monday.