Bring my own device and protection plan

I'm looking for a newer phone, but it's cheaper to buy the unit where I work.  I know how to transfer the sim card, but can I add a protection plan for this device if I buy it other than at T-Mobile?  I love T-Mobile, and they've been great, but with my employee discount where I work, the difference in price is quite significant.  However, T-Mobile's insurance plan is better/easier to make a claim.  Thanks for any insight!