Research In Motion may have sold more BlackBerry PlayBook tablets than analysts expected, as many as 50,000 on the first day alone, according to RBC Capital Markets analyst Mike Abramsky.

In a research note sent to investors yesterday, Abramsky said he and his team checked with 70 different retail stores, including Best Buy, Staples, and RadioShack outlets, to ask about PlayBook sales on the first day. The team found a range of responses from light sales to 11 percent of the stores sold out, but overall leading to an estimate of 50,000 sold on opening day this past Tuesday, including presales.

Abramsky also used Best Buy's online inventory tool to check 180 other retail stores, according to Boy Genius Report. That analysis found the 16GB version of the PlayBook unavailable at 13 percent of the stores, the 32GB edition unavailable at 87 percent, and the 64GB model unavailable at 91 percent. Of course, as BGR points out, these figures alone can't tell the whole story because they don't indicate how many units of each model were initially in stock.

Abramsky believes the PlayBook's launch may have been stronger than those seen for both the Motorola Xoom and the Samsung Galaxy Tab. Overall, the analyst expects RIM to ship 500,000 PlayBook tablets during its first fiscal quarter, ending in May.

The PlayBook has earned a fair share of negative reviews based on some of its current shortcomings. Abramsky believes some of those issues may be largely resolved through wireless updates and new 4G versions of the tablet that RIM is planning for later this year.

Currently available in a Wi-Fi-only version, a 4G edition of the tablet is headed to Sprint this summer. RIM is also planning 4G versions that can run on Verizon Wireless's LTE network and the HSPA+ networks from AT&'T and T-Mobile (PDF).

For now, however, the company is running into some initial difficulties with both AT&'T and Verizon.

AT&'T has so far refused to support RIM's Bridge app that lets BlackBerry users pair their phones with the PlayBook over AT&'T's 3G network. That piece is critical, as RIM has been touting the syncing capabilities between its BlackBerry phones and the new tablet.

Verizon seems to be on the fence about carrying the PlayBook at all, despite RIM's initial expectations. Verizon Wireless spokeswoman Brenda Raney sent CNET the following statement:

"We are still evaluating the Blackberry Playbook and have not made a determination as to whether or not we're going to distribute it."

Abramsky believes that the AT&T Bridge issue will need to be resolved before the PlayBook can reach "critical mass." Even further, RIM has to achieve some momentum with its own mobile app market at the same time that more testing of the tablet is done among potential enterprise adopters.