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Thank you. With the neatrom I tried XXEMG4 modem (I'm not sure but I think) and the problem was present...
Android 4.1.2 official (stock) : OK
Android 4.3 (stock) : problem --> slams at the first call (and only the first call) after the boot.
Android 4.4.2 (different versions tested): no problem with slams but sound quality during a call is bad --> saturation