In EM, can you check the network registration status?
First step would be to determine if this is device-side, or if being rejected by the tower due to IMEI or other mismatch.
I speculate it’s the former, in which case it’s probably different RF front-end (as mentioned by ars18)…
Some research suggests that it’s not so simple after all.
While the SoC might be the same, there are other physical components that contribute to radio capabilities.
Some of these sit outside the SoC. Like the radio front-end (RFFE) which contains the specific hardware filters and duplexers for the supported frequencies, and sometimes, the transceiver which sits between the SoC and RFFE.
So, seems like it’d be impossible to swap from Fossibot to F25 but theoretically would work the other way around. Simply because the Qin doesn’t contain the hardware support for all of the bands.
(Some difference is the PAMiD vs FEMiD chips present in the RFFE of these phones. The former is for premium connectivity like the Fossibot and the latter for lowend cost-efficient devices like the Qin).
Check out https://www.mediatek.com/hubfs/MediaTek%20Assets/Pdfs/White_Papers/LTE-RFFE-for-Mass-Market.pdf
I don’t think the reason is the mismatch. @BenTorah is probably right that it’s a hardware mismatch with different rffe. I still think that if someone who has experience with ghidra were to inspect both binaries, I believe some bands can be enabled but it’s not an easy process. The question is if the f22 does happen to have the exact same rffe as this. (I don’t even know the chipset of the f22)
If anyone wants, I posted both firmwares. You can play around with ghidra, test on f22 or just do whatever you want with it
@flipphoneguy I just came around this topic don’t have time to read all the previous posts just tell me in the end you managed to flash the F 25 to work in the USA or not?