BlackBerry PlayBook sales hit 50,000 for the first day of US sales on April 19, including pre-sales, an analyst at RBC Capital Markets estimated.

Overall, Research in Motion (RIM) is on track to sell 500,000 PlayBooks in its first fiscal quarter ending in May, analyst Mike Abramsky wrote in a note to his clients that was reported in the Montreal Gazette .

Abramsky's staff checked 70 retails stores and found 11% of the locations that stocked the device had sold out. "The launch appears to have been stronger than the launch of Motorola's Xoom or the Samsung Galaxy Tab, although it's too early to judge sustainability," Abramsky wrote.

In suburban Boston, one Best Buy outlet had only one 16GB PlayBook on sale for $499.99 the first day; it was also being used as a demonstration model. A nearby Radio Shack sold all three PlayBooks it had on the first day, a clerk said.

Several analysts said that RIM was probably relying on pre-sales of the device to business customers, although business sales were said to be direct from RIM to customers and not through retailers .

The PlayBook has been criticized for not including a native email client, forcing users to rely on a Web-based email account. Users can also tether to a BlackBerry smartphone for access to corporate mail through BlackBerry Bridge software on the PlayBook and its connection through the phone to a BlackBerry Enterprise Server.

AT&T is still testing the BlackBerry Bridge software, meaning that tethering through an AT&T BlackBerry phone is not yet supported. AT&T, Verizon Wireless and Sprint have not announced when they will sell the PlayBook, but Wimax (Sprint), LTE (Verizon) and HSPA+ (AT&T) versions of the tablet are expected from RIM this summer.

RIM is also planning to offer a free over-the-air update to PlayBook with a native email client this summer.

Even though Verizon spokeswoman Brenda Raney told Computerworld on Tuesday that Verizon has "not announced when we will sell the PlayBook," she told CNET on Wednesday: "We are still evaluating the Blackberry Playbook and have not made a determination as to whether or not we're going to distribute it."

In comments yesterday, Raney confirmed that Verizon has not yet decided whether it will carry the PlayBook.