iPhone 8 purchased through AT&T change to T-Mobile

I was able to purchase an iPhone 8 through my company with AT&T being the carrier. I have since left the company and would like to use the phone with a T-Mobile plan. When I put the T-Mobile SIM card in I receive the message Not Unlocked for that Network. Any suggestions on how to make this work or can I use the phone w/AT&T only?

Solution 1:

Your original provider Controls the network lock status.

• https://www.att.com/deviceunlock/

Procedures differ per other providers, but for you, start at AT&T to check your lock status or request it be changed.

Solution 2:

If I do not misunderstood your question, you're looking for a way to un-"simlock" your phone. There are many ways to do this:

• Make sure to check if you're sim-locked for a given period, or forever.
• Call AT&T provider and explain them the problem to normally get the network unlocked. It can differ with each provider.
• (NOT RECOMMENDED!) Try to google something like "unsimlock jailbreak ios" + your ios version to check if you can't just do it this way, if the provider does not answer or solve your problem...

Hope you solve your problem!
Léo