Iphone 3g, 4.21, 6.15 gps fix?

i helping friend unlock iphone 3g. realize on 4.21 firmware, modem 5.15 , bootloader not downgradeable. choice unlock phone know of go 6.15 ipad baseband. know kingdom come of iphone, no chance of going back. heard story if updated 6.15, there chance gps stop working , rumor claim if downgrade phone firmware 3.12 , baseband of 6.15 , gps still work. can confirm it?

 

even if downgrade os, gps still fried.

 

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