How can I tell if my iPhone is locked

Grumpy.grandad wrote:

Somewhat helpful. But I don't see an answer to my question.

I want to check to see if this phone is locked to a carrier. Should I swap Sim's to see if I can make a phone call?

Or is there somewhere online I can check the IMEI number?

Ah, so you were seeking a carrier lock, and not information about Activation Lock or the IMEI blacklist or the plethora of other ways to get ripped off. Activation Lock and IMEI blacklist locks are how most folks get ripped off, including phones sold and initially working and then later blacklisted.

An iPhone that is not locked to a carrier will show that in Settings.

Unlocked: Settings > General > About > Carrier Lock > No SIM Restrictions

There are sketchy and scam websites seeking to collect IMEI information, too.

See the pre-purchase checklist here:

.ll The All Too Common SAD Reality of Buying a used iPad/iPhone - Apple Community

There are various scams here, and selling a locked phone is just one.