An estimated 250,000 BlackBerry PlayBook tablets have been sold in the first month, edging out Motorola Xoom's early sales, an analyst at RBC Capital Markets said.

Motorola Mobility said in late April that it sold 250,000 Xooms in the first five weeks it was on sale, which were Xoom's entire sales in the first quarter of 2011.

The PlayBook sales estimate, included in a note from RBC analyst Mike Abramsky, came after recent checks were conducted at 180 Best Buy locations in the US, where 84 percent of the 64GB PlayBooks were sold after first going on sale April 19 .

Abramsky said Research in Motion might sell 500,000 PlayBooks in its first quarter.

Critics have discounted RBC's overall analysis of RIM , given that RBC (Royal Bank of Canda) Chief Operating Officer Barbara Stymiest also sits on RIM's board of directors .

However, Abramsky has done the most thorough checks on sales of PlayBooks and recently downgraded RIM's stock, citing RIM's expected slowdowns of smartphone sales in the US and Latin America.

Abramsky's latest note also indicates that RIM smartphone shipments could drop by 9 percent, to 13.5 million devices, when RIM gives its first fiscal quarter earnings report June 24.

RIM now has the lowest number of smartphone models on sale at US carriers since mid-2007, Abramsky noted.

Despite a RIM recall of 1,000 PlayBook s earlier this week, Abramsky said his retail store checks show that customer returns of the devices "are nominal."

The ultimate success of the PlayBook could depend on many factors, analysts have noted, including how soon RIM delivers a promised free upgrade that provides native email and when US carriers launch 3G and 4G versions of the tablet.