Are we talking about *phones* or about gadgets?
If you're in the same hemisphere as me, I can give you a hint about *phones* with autonomous IMEI editing capabilities, mostly CAT or Alcatel branded, like CAT B40 or Alcatel 3025X. Combine this with anonymous prepaid SIMs like LycaMobile and you're good to go.

If we're talking about *gadgets* then your best bet is either Graphene'd Pixel with anon eSIM like silent.link and/or a dedicated data-only WiFi-enabled modem and using SIP numbers for actually calling somewhere, or a very hard way of picking and debloating a smartphone with editable IMEIs and then see the first part of my post.