BlackBerry CEO John Chen has said that he is "outraged" by a recent campaign by T-Mobile that offered its Blackberry customers the chance to switch their phones to an iPhone 5s.
The mobile network sent an email to customers in the US last week advertising the chance to upgrade their BlackBerry devices to the latest iPhone model free of charge.
In a blogpost published yesterday, Chen wrote that T-Mobile had not consulted BlackBerry before making the offer, referring to it as an "inappropriate and ill-conceived marketing promotion".
"To T-Mobile, I would like to remind you that our long-standing partnership was once productive and profitable for both BlackBerry and T-Mobile," Chen wrote.
"I hope we can find a way forward that allows us to serve our shared customers once again."
Some of the T-Mobile customers who received the offer sent messages via social media to their network provider criticising the promotion.
"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," Chen added.
"Your partnership with our brand is appreciated by all of us at BlackBerry, and draws a sharp contrast with the behaviour of our longtime business partner."
T-Mobile has since apologised publicly to BlackBerry, iterating that it is "happy to be a BlackBerry partner".
In a statement released yesterday, T-Mobile spokesperson Anne Marshall said: "As an additional courtesy to our BlackBerry customers, we will begin offering free expedited shipping of BlackBerry devices by Friday."