Add line for phone promo then cancel other line, will the promo stay on new line?

No it will not.  You can't cancel a line 3 months prior to the promotion and until the end of the time specified on the promotion if you take it. The last one was a 2 years from what I remember.

I noticed that Tmobile is tightening down on the loopholes.

I remember when they gave 2 lines free and a lot of people picked them up and cancelled the old lines.  Then I guess that's when they realized they messed up.

I am also dealing with a similar situation. I want to know how much the service bill for this month be. Will it be the amount with the additional line added?

You would need to look at the fine print of the offer.

Just wondering if anyone has had the same situation.. 

This is basically a user to user forum with some tmobile moderation that don't have account access so you need to contact Tmobile support using messenger on one of tmobile's social media platforms to see if they can help you they also are a higher tier of support.

BuggyBear wrote:

Hi, I was wondering if I get a phone at a promo price for adding a new line what happens if I later need to cancel another line (not the newly added one), would that affect the promo credits for the new phone? Gracias 

As far as I understand it they have a promotion where you get a third voice line at no additional cost. I don't know if that would help but that's what I know. 

generally there is a time limit.  It should be in the terms.  From some of the other promotions some you couldn't have gotten rid of any lines 3 month prior to the promotion to 6 months after the promotion.  Make sure you read the terms.

terminating a line to get an add a line promotion isn't going to happen just an FYI as there are terms for that specifically.