How can I find if a phone is locked or unlocked?

I got a used Alcatel SmartFlip 4052R. Is there a way to find out if the phone is locked or unlocked? I entered the IMEI in several IMEI checkers, but all those said was that the phone is clean and not blacklisted/stolen. BTW, the phone has a SIM card in it. Should I remove it before I power it up?

UPDATE: I removed the SIM. It says "AT&T PREPAID Nano 6209B".

The way I usually check would be to insert a T-Mobile SIM card. A T-Mo MVNO is fine, and the SIM doesn't need to be active. If you don't have one, Simple Mobile and Tracfone SIM kits are available at a lot of stores for $1. For the Tracfone kit, use the pink T--Mobile compatible SIM.

If the SmartFlip doesn't reject that SIM, it should be unlocked.

I have a Tracfone 3-SIM kit somewhere. I'll put in the pink one. Thanks KentE!

PS. Do they have to make the SIM cards so small? NanoSIM! Yikes.

Be happy you don't have to ever handle an eSIM!!
eSIM size is 2,5mm by 2,3 mm, and the thickness is 0,2 mm.

For comparison the nano-SIM or 4FF is 8.8 mm by 12.3 mm.

A regular SIM or 2FF (Second Form Factor) measures 15 mm by 25 mm.
The micro-SIM, or 3FF SIM card is 12mm by 15mm and 0,76 for thickness.

If don't have a full-size sim card for that particular phone or don't want to stop by Tmobile for them to check, you can call the carrier directly:
"Call the customer service number of your carrier to ask whether your phone is unlocked. Here are the phone numbers for the major wireless carriers:

AT&T: 1-800-331-0500
Verizon: 1-800-922-0204
T-Mobile: 1-877-453-1304
Sprint (now part of T-Mobile): 1-866-275-1411
Got the tip from this article:

And I thought a NanoSIM was small. Each side of the eSIM is roughly 4 times smaller!

Why they do that? People surely don't want them so small? Is it to discourage changing them?

Thanks for the info. I might have to unlock it.

I was sorta kidding - eSIM is an embedded SIM so it is really a component of the phone and not meant to be user accessible.
As to why, well the constant drive to miniaturize and pack in more power/higher spec./more features. Consumer can switch carrier quicker (no wait for SIM). Time will tell re downsides, I suppose eSIM allows more carrier control of your device but I'm really not sure on specifics.

Oh, it's not meant to be user accessible. I understand it then. ...

... And it's perfectly fine. If I don't have to put it in or take it out, they can make it invisible AFAIC!

That's sure is better than SIMs. Do you have to use SIMs at all in an eSIM phone?

I think all phones currently available with eSIM have one slot for a normal SIM, + the eSIM.
The catch is that eSIM activation is only available (in the USA) directly from the big 3 carriers, plus a few MVNOs at this point.
The primary phones with eSIM capability are recent iPhones, Pixels (starting with Pixel 4?), and one or 2 flagship Samsung devices. Some providers only support eSIM on the iPhones.

Pixel 3a has an eSIM also.
I'm not sure about the Pixel 3

Fun fact (at least, I thought it was fun when I learned it): As you might have guessed from redrotors's post mentioning a 2FF, 3FF, and 4FF, the credit-card size that you often punch the size you need out from these days with BYOP kits is actually 1FF and was the original full-size; 2FF was originally "mini..." but 1FF has practically disappeared from use by now.

However, if you have reason to encounter some other kind of smart card in that size, you might notice that the dimensions and contact position are quite familiar.

Thanks for this, and you kept me from (eventually) looking it up to find the missing 1FF!

credit card size? that sounds ...a little big! I vote for 1.5FF!

I looked it up!

Hmmm, the eSIM isn't 2.5mm x 2.3mm as redrotors said. The quoted eSIM dimensions must be wrong?

I put the Tracfone pink T-mobile SIM in and rejection. All right! The SmartFlip is unlocked!

Since this phone will be used more than mine, I'll put my free FreeUp SIM there (in the Alcatel SmartFlip), and I'll order a truPhone SIM for my very seldomly used cell phone (Sonim XPS5XP5). Any reason my plan won't work?

Unlocked or not, the Alcatel SmartFlip looks well suited for AT&T MVNOs (including FreeUP, with LTE bands 2, 4, 5,12-- and it's on the list for AT&T VoLTE moving forward.

Does Truphone still run on the AT&T network?.

I checked the SmartFlip's IMEI at FreeUp's BYOS checker and it said:

Is the unlock mention not a real requirement?

One of the reasons I chose it! (list)

Yes, see link.

Thanks, dst11 ! It looks like you picked wisely with the SmartFlip-- which shouldn't surprise me, because I remember you were likewise diligent in researching before buying your Sonim.

With TruPhone still on the AT&T network, I think your plan on which service to use with which phone is just fine.

re: unlock requirement: AT&T's policy on their Prepaid- and Postpaid- branded phones is that they allow them to be used on AT&T MVNOs even if they are still locked. (But note that some individual providers may be more restrictive than AT&T's 'allowed' policy.) Knowing that your SmartFlip is unlocked is still a good thing, since that policy could change or you might want to take it elsewhere..

So, in regards to the FreeUP warning:
An AT&T-branded phone could be used even if it is still locked to AT&T.
Any other branded device would have to be unlocked from it's original provider.

Thanks KentE! Like you, IIRC, I don't want to add to my collection of obsolete cell phones. I already have 2, the 2 Kyocera DuraXTs, and soon it will be 3, the Sonim XP5. I incorrectly wrote XPS5 and not XP5 above. The XP5, unlike the XPS5 and the XP3, doesn't do VoLTE. I suspect you have more than 3 obsolete cell phones!

I think truPhone requires an unlocked cell phone. But truPhone isn't a true ATT MVNO right?

When you say "Any other branded device" you mean 'Any device locked by any other provider' right?