If the phone is sold by the mobile service provider, only the mobile service provider can get it unlocked. Mobile service providers who sell phones usually at a lower price to attract customers so they don't want you to purchase their phone at a lower price and then go to another provider for service.
However, at the end of the initial service contract, (a year or two) you might be able to switch providers. I say might because legislation in that regard is fairly recent and may defer from one state or country to another. You should inform yourself.
I just came across this ad: "Brand:Motorola Model:Motorola Moto e4
MPN:MOT1766BLK Contract: Without Contract Now, with that said, could I purchase this device with the understanding it is 'unlocked" or could be since there is "NO CONTRACT"?