[Frank999]

I know the answer to the following question is "contact T-Mobile" but I just want to be sure I'm not wasting my time.
Here's my situation. I currently own the Google Nexus 5x. Unfortunately it's fallen victim to the boot-loop issue that has plagued this model. The phone is no longer under warranty and from what I can gather there is no easy fix for the problem. So, I went ahead and order a new Google Pixel phone. The problem is that the delivery estimate is not until June 20-27 which leaves me sans phone until then. I do however have an older Nexus 4 phone lying around that still has a T-Mobile pre-paid sim card in it. I did try activating it on the T-Mobile website but got an invalid number error message. I guessing this IMEI number is invalid because it was deactivated when I ported my number over from the N4 to the N5x.
So to finally get to my question, is it possible to activate this phone to use until my new phone arrives at which time I will activate that phone with T-Mobile.
Thanks in advance.

[underway99]

The number and account are resident in the SIM, not the device. So long as the SIM from your 5x is the same size as the SIM for your N4, it should just be a matter of putting the active SIM into the N4. Make sure that you power down both devices before you pull the SIM from the 5x and install it into the 4. Power it up and you should be good to go.

If the SIMs are different sizes, then a trip to a TMO store for a new SIM should get you fixed up.