just did a test to playback a wav file on voice call in LTE network.
It is working fine.
AT!AVAUDIO=3,1,/home/root/0-to-9_8k.wav
OK
at!avaudio=3,0
OK
NO CARRIER
ati3
Manufacturer: Sierra Wireless, Incorporated
Model: WP7607
Revision: SWI9X07Y_02.25.02.01 000000 jenkins 2019/01/30 08:13:05
IMEI: 359779081234565
IMEI SV: 6
FSN: VN730485080103
+GCAP: +CGSM
OK
at!gstatus?
!GSTATUS:
Current Time: 2828 Temperature: 34
Modem Mitigate Level: 0 ModemProc Mitigate Level: 0
Reset Counter: 1 Mode: ONLINE
System mode: LTE PS state: Attached
IMS reg state: NOT REGISTERED IMS mode: Normal
IMS Srv State: NO SMS,NO VoIP
LTE band: B3 LTE bw: 10 MHz
LTE Rx chan: 1851 LTE Tx chan: 19851
LTE CA state: INACTIVE
EMM state: Registered Normal Service
RRC state: RRC Idle
PCC RxM RSSI: -84 RSRP (dBm): -106
PCC RxD RSSI: -95 RSRP (dBm): -130
Tx Power: 0 TAC: 0462 (1122)
RSRQ (dB): -5 Cell ID: 06745D15 (108289301)
SINR (dB): 15.6
OK