BlackBerry CEO John Chen is not happy. Not at all. He slammed T-Mobile for teasing its customers to switch to Apple iPhone. Loyal fans of the brand also ganged up on the 'Uncarrier' in social networks and online forums.

T-Mobile pitched an iPhone 5s to BlackBerry users last week via email, tempting them to "get the tools to do more" for a $0 down scheme.

"Great offer for BlackBerry customers," the banner of the ad stated. "Switch to iPhone 5s and get powerful communications and productivity apps -- with the ease of use that Apple is known for."

For a brand that has been struggling to please the market, T-Mobile's move is another big challenge for BlackBerry. It's CEO has been cleaning up its rolls of top executives, selling real estate properties of the company, and looking for possible deals that might give the brand a fighting chance in a tough market.

"I want to thank our loyal customers for your commitment to BlackBerry. By expressing your outrage directly to T-Mobile ‎through tweets, calls and comments in the media and on blog posts, you sent a powerful message that T-Mobile could not ignore. Your partnership with our brand is appreciated by all of us at BlackBerry, and draws a sharp contrast with the behavior of our longtime business partner," Chen wrote on the company's official blog. "I can assure you that we are outraged too. What puzzles me more is that T-Mobile did not speak with us before or after they launched this clearly inappropriate and ill-conceived marketing promotion."

BlackBerry loyalists also vented their feelings about the offer of T-Mobile online forums, prompting T-Mobile CEO John Legere to respond in a series of tweets.

"BlackBerry users, I'm hearing you loud and clear. Let me work with the team and get back with you," Legere tweeted.

BlackBerry users, I'm hearing you loud and clear. Let me work with the team and get back with you.

— John Legere (@JohnLegere) February 16, 2014

It seems Legere found out that it's not a goo idea to upset BlackBerry fans. "BlackBerry follow up- We give our customers choices, but you don't have to give up your #loyalty. We will continue to support," he said in another tweet.

BlackBerry follow up- We give our customers choices, but you don’t have to give up your #loyalty. We will continue to support — John Legere (@JohnLegere) February 17, 2014

For T-Mobile, BlackBerry is dead and it has been removing its range of smartphones from its stores since September, although it still gives loyal customers of the QWERTY keyboard-equipped handsets the option to ship the devices directly to their address.

Aside from thanking its loyal customers, Chen also addressed T-Mobile directly.

"...I would like to remind you that our long-standing partnership was once productive and profitable for both BlackBerry and T-Mobile. I hope we can find a way forward that allows us to serve our shared customers once again. Notwithstanding the current challenge, we remain very excited about BlackBerry's future," he wrote.

Looks like Legere singed his fingers on this one.