I want to sell a Lumia 925 and need to know if it is SIM Locked. Is it possible to find out if it is without using a SIM card from another provider (which I don't have)?
I don't know if this can help but at least in Lumia phones in extra+info there is a "Manufacturer Name" and "Mobile Operator".
I think one of them can have information about the carrier and maybe it will tell you if it is associate with the carrier.
In my unlocked Lumia 920 I have this info:
You can see RM-821-lta-brazil_253 that maybe can have carrier info in your case.
I believe the mobile operator give your more clue about this, in my case it says only 000-BR. I think in case of carrier lock this 000 would changed to carrier number.
All this info is speculative. Here in Brazil is illegal lock the user to a carrier so they are not locking phones anymore (as far as I know) just making you sign the x years contract.
I found new information with help of Windows Central.
Basically it points to a official Windows Phone Dev article titled Registry values for carrier-unlocked phones
There you can see that, in my case, 000-BR is a unlocked version for Brazil.
You just need to go to extra-settings and see which is your Mobile Operator and found in the list.