What's the difference between an unlocked smartphone and a locked smartphone and which is better to own?

Unlocked phones can work on any GSM carrier worldwide.

Locked ones can only work on 1.

Aside from that (if comparing the same phone model) they are the same. Of course the unlocked phone would hold higher resale value.

If you don't plan on switching carriers anytime soon (like say 2 years (usual timeframe people hold on to a phone these days)) then getting an unlocked wouldn't really matter.

Locked phones can be a big problem if you're purchasing it. You may never be able to use it, especially if it has been reported stolen or lost. An unlocked phone can only be used with a network that has the same network protocol (GSM or CDMA) as the phone. Unlocked iPhones can work on either type of network.

unlocked phones can work on any gsm carrier worldwide...

locked ones can only work on 1...

aside from that (if comparing the same phone model) they are the same... of course the unlocked phone would hold higher resale value...

if you don't plan on switching carriers anytime soon (like say 2 years (usual timeframe people hold on to a phone these days)) then getting an unlocked wouldn't really matter...

Locked phones are tied to a specific network, it will only work on that network unless you pay the network to unlock it for you.

An unlocked phone will work with any network, this means you have the freedom to choose your network. It also helps when selling it in the future as people prefer unlocked phones

A locked phone is locked to a specific phone carrier and you can only use it on that network. An unlocked phone can be used on any network.

If it's locked you can't change providers without paying to get it unlocked.

it's illegal to have an unlocked smartphone... nobody shall cover any damage... you shall not receive updates on most phones either...

It's illegal to have an unlocked smartphone. Nobody will cover any damage. You will not receive updates on most phones either.