Sophia Cheng bought her first BlackBerry, a red Curve, in 2007, and has been a loyal user ever since.

Now Ms. Cheng, a 31-year-old public-relations consultant from Vancouver, British Columbia, is considering a switch to a Google Inc. (GOOG) Nexus smartphone. The only reason she hasn't yet: She wants to test the new BlackBerry, 'the one with the keyboard,' she says.

Earlier this year, Research In Motion Ltd. (BB.T, BBRR) launched a touch-screen phone three years in the making, the BlackBerry Z10. While the success of that rollout is still uncertain, RIM is gearing up for its second act of 2013: the debut of the keyboard-equipped Q10.

The device will hit Canada and the U.K. first, and the U.S. after that. U.K. carriers have said the maker will start shipping phones as soon as Friday, while in Canada carriers and retailers like Best Buy Co. (BBY) will begin selling the phone on May 1, RIM said Tuesday.

The Q10 looks similar to the once-popular BlackBerry Bold, which was introduced in 2009 and was the last phone to run on the company's old operating system. It will have both a classicphysical keyboard and a small touch screen and will run on RIM's new operating system, BlackBerry 10. Carriers and retailers are advertising the device at roughly $200 with a multiyear plan, putting it in line with other high-end devices on the market.

RIM is counting on keyboard-loving users like Ms. Cheng to snap up the new model. There is still a big market out there for keyboard-equipped smartphones, and RIM dominates it. The big problem: It is shrinking fast.

Last year, IDC estimated that the world-wide keyboard smartphone market was 62.8 million units, down from 100.2 million units in 2011. RIM's share of that market is 47%, according to IDC.

Nokia Corp. (NOK1V.HE, NOK) has long been a strong player in the keyboard market, and more recently Asian phone makers like Samsung Electronics Co. (005930.SE, SSNHY) and Huawei Technologies Co. have also started pushing more keyboard-equipped phones into developing countries.

The market for touch-screen-only phones, meanwhile, jumped from 372 million units in 2011 to 650.1 million units last year, according to IDC. RIM's share of that pie: 3%.

RIM executives say they understand the shift. That is why they chose to roll out the all-touch Z10 ahead of the Q10, they say. RIM can count on a loyal following of keyboard-using customers, but it had to make an extra push for its touch-screen device. Chief Executive Thorsten Heins also said RIM knew the all-touch Z10 was probably better suited to succeed in the exploding 'bring-your-own-device' market, in which workers are increasingly using their personal phones for work.

Still, the decision baffled some customers and carriers.

'I do wish they came out with [the Q10] first or at the same time,' Ms. Cheng says. 'I think a lot of people are on the fence and want a new phone, and they may have made their decision already. I don't know why it took so long.'

When RIM told carrier partners months ago that it would be launching the Z10 first, carrier executives expressed disappointment that both phones wouldn't be coming out at the same time, according to people familiar with the matter. When they asked for clarification about the staggered-launch strategy, RIM executives didn't elaborate, according to these people.

'Our approach to launching BlackBerry 10 was to focus first on bringing our all-touch BlackBerry Z10 smartphone to market, and then follow with the 'qwerty' BlackBerry Q10,' a RIM spokesman said in a statement.