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BlackBerry CEO John Chen called T-Mobile's offer a 'clearly inappropriate and ill-conceived marketing promotion.' (Brendan McDermid/Reuters)

​BlackBerry CEO John Chen is angry the U.S. carrier T-Mobile offered BlackBerry customers an upgrade to an iPhone for no money down.

In a blog post titled "BlackBerry's Reponse to T-Mobile's Anti-BlackBerry Campaign" Chen thanked customers who expressed their "outrage" about the offer on social media.

"I can assure you that we are outraged too," Chen wrote on the Inside BlackBerry blog Tuesday. "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."

He added that BlackBerry is working on an offer designed especially for its loyal customers on the T-Mobile network.

T-Mobile, the fourth largest wireless carrier in the U.S., emailed some BlackBerry customers last week with what it billed as a "Great offer for BlackBerry customers."

The email told customers to "Get the tools to do more" and offered an iPhone 5S, Apple's latest model, for no money down. Customers instead would pay $25 a month for 24 months to purchase the phone (for a total of $600.) The 16 GB version of the phone usually retails for $649 and the 32 GB version for $749 in the U.S.

Chen wrote that he wanted to remind T-Mobile that "our long-standing partnership was once productive and profitable" for both parties and he hoped the two companies could "find a way forward that allows us to serve our shared customers once again."

In a statement emailed to CBCNews.ca on Wednesday, T-Mobile said  it is "happy to be a BlackBerry partner and apologize for any confusion."

T-Mobile added that as an "additional courtesy" to its BlackBerry customers, it will start offering expedited shipping of the devices by Friday.

T-Mobile

T-Mobile, the fourth largest wireless carrier in the U.S., e-mailed some BlackBerry customers last week with what it billed as a "Great offer for BlackBerry customers." (Crackberry blog)