To be frank, playing with region 41 is probably not the best place to start self-education on modding Garmin devices. Unless you know exactly what you're doing, it is very easy to brick a device with a corrupt rgn41. You've lost the model number by playing with it, maybe some features have also been compromised but 2457 is a junior basic-featured model so probably none are lost. But you've avoided bricking however certainly 'confused' it. So my first advice is to flash back the original 41 [i assume you made a backup 41.bin]. Before flashing back you should [Only registered and activated users can see links. ] and then clear it again after reflashing your original 41.bin. If you don't have a backup, hopefully reversing the changes in hex and reflashing will fix it [but make a backup before that of course].

You're correct in that the 24x7 and 25x7 range do share basic hardware and use the same firmware [unit software], therefore in theory it should be possible to enable some of the lacked features. However the senior models have hardware fitted which is not present in the juniors. BT module and perhaps microphone for instance. Your 2457 lacks BT hardware and probably therefore it doesn't have a mike. If it does have a mike or one can be fitted then you maybe can activate ASR. Of course no 24x7 4.3" unit can become a 25x7 5" unit so i think you should be comparing your 2457 to 2497, and aspiring to some of it's features [2497 is identical to 2597 in features anyway].

Code:
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If you click the Blue 'Show only Differences' button on that page you'll see that apart from the obvious physical difference for BT the only listed ones from 2457 to 2497 are ASR and Smartphone link.

Adding a BT module is in the 'too hard basket' imho, but for ASR adding a mike if it's not present should be easy enough [see Post #129 of [Only registered and activated users can see links. ] for the basic how-to]. Modding rgn140 is a cinch to 'enable' the extra features. Now comes the really hard part, the firmware probably needs to be modded to make the ASR Icon visible in the Apps screen of your 2457. That's if other experiences in regard to the missing icons are an indication. So if you really wanna get down 'n' dirty seeing you have firmware experience you may want to try reverse-engineering the firmware to see what might be stopping the Apps icons showing. Make sure you use the correct fw as there are 2 HWIDs for 2xx7/8 series, your 1582 and 2077: [Only registered and activated users can see links. ].