Edited to add: After 24 hours with neither phone working, I called tech support, and they managed to get it working. The first thing they told me was that the SIM card number I supplied had already been activated. I still had no service on the phone, though. At their request I powered it down completely, then turned it back on, and voila, I had service. So if this happens to you... try that.
I have been a Tracfone customer for at least 15 years. My most recent activated phone has been a Samsung Galaxy J7 Crown Tracfone, which I've used for about 2 years. Recently I've been getting the "File system limit, too many files have been created on your phone" message, I'm getting a popup that says the Samsung Experience Service (whatever that is) has stopped, and as of yesterday the wifi will not turn on, so the only way to put the phone online is via mobile data. All the advice I could find online recommended a factory reset. I haven't done that yet, as I am not entirely confident that I've managed to back up everything on that phone that I'm going to need.
And because I'm pretty close to "hitting the storage wall" with this phone anyway, I decided it's time to replace it. I've purchased an unlocked Motorola Moto G Power and a Tracfone SIM kit. I've installed the SIM card (and an SD card for extra storage). Last night I went through the activation process online, requesting to transfer service to the new phone and keep my current phone number, and entered the new SIM card's number as requested. The final on-screen message advised me that the transfer of my phone number to the new phone could take anywhere from a few minutes to a couple of days.
As of this morning, neither phone is receiving calls or texts, nor will either phone make outgoing calls. I dialed my cell number from my land line phone, and without either cell phone having even rung, I got a recorded message saying that the user (that would be me) has not set up voice mail. (I set up voice mail years ago.) When I try to make an outgoing call to my land line on the old cell phone, the call ends within one second of dialing (and the land line doesn't ring). Trying the same thing on the new cell phone, I get a message that this phone is not set up for voice calls.
Is this normal behavior when transferring one's number to a new unlocked phone, or has something gone wrong?
Edited to add: My Tracfone account page shows that the old phone's last day of service was today, and therefore it will no longer go online with mobile data. And the new phone is still not activated.