Research in Motion's foray into the tablet space is getting more gloomy as Sprint closed the door to its 4G Playbook tablet.

The nation's third largest mobile provider said there wasn't much interest from potential business clients.

"We apologize for any inconvenience but the BlackBerry 4G PlayBook tablet that was announced in January for summer availability will no longer be coming to the Sprint network," the company said Friday.

The loss of a Sprint deal adds to RIM's woes. The Playbook has not gained support from Verizon or AT&T either. That will also disappoint consumers looking for something that can work beyond WiFi connections, or do not have Blackberry's to tether to.

RIM characterized the 4G PlayBook change as a reflection of its new focus on Long Term Evolution, or LTE wireless standards, but still hopes to push 4G tablets later this year.

"Testing of BlackBerry 4G PlayBook models is already underway and we plan to enter labs for network certifications in the US and other international markets this fall," the company said.

The setback highlights the struggle RIM is having as it tries to push into a tablet market dominated by Apple.

While the analysts predicts worldwide tablet computer market to 60 million units this year, up from 55 million previously, Apple should command almost 40 million units, or 66 percent of the market.

In contrast, the Blackberry maker cut its Playbook tablet shipment estimates to 2.5 million from 3.6 million for the entire year.

The move also deals a blow to RIM's overall fortunes. It's staple Blackberry smartphone is losing market share and mindshare among consumers.

RIM's growth in international markets was not enough to offset its decline in North America for Q2.RIM shipped 13.2 million smartphones representing an 11 percent quarter-over-quarter drop.

RIM is now the No.4 smartphone vender behind Apple, Samsung and Nokia.