What I do is simply calling A -> B. In the moment of accepting the call SIGSERV happens with the following trace:
I/DEBUG (29934): r0 753686ce r1 40000000 r2 753686ce r3 00000190
I/DEBUG (29934): r4 63fbfc58 r5 00000002 r6 63fbfc58 r7 400db000
I/DEBUG (29934): r8 401569c4 r9 65864000 sl 63186b68 fp 65961a50
I/DEBUG (29934): ip 00000004 sp 65961a20 lr 40104040 pc 4010406c cpsr 20010010
I/DEBUG (29934):
I/DEBUG (29934): backtrace:
I/DEBUG (29934): #00 pc 0001506c /system/lib/libc.so (dlfree+1128)
I/DEBUG (29934): #01 pc 0000e1c8 /system/lib/libc.so (free+20)
I/DEBUG (29934): #02 pc 00010b14 /data/app-lib/com.myapp-1/libortp-armeabi-v7a.so (ortp_libc_free+20)
I/DEBUG (29934): #03 pc 00010034 /data/app-lib/com.myapp-1/libortp-armeabi-v7a.so (ortp_free+44)
I/DEBUG (29934): #04 pc 00023da0 /data/app-lib/com.myapp-1/libortp-armeabi-v7a.so (freeb+140)
I/DEBUG (29934): #05 pc 00023e6c /data/app-lib/com.myapp-1/libortp-armeabi-v7a.so (freemsg+56)
I/DEBUG (29934): #06 pc 0000bcb4 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (ms_bufferizer_read+352)
I/DEBUG (29934): #07 pc 0008e8e8 /data/app-lib/com.myapp-1/libmediastreamer_voip-armeabi-v7a.so (ms_opus_enc_process+1600)
I/DEBUG (29934): #08 pc 0000b0c4 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (ms_filter_process+72)
I/DEBUG (29934): #09 pc 0000e524 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (call_process+144)
I/DEBUG (29934): #10 pc 0000e340 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graph+112)
I/DEBUG (29934): #11 pc 0000e3a8 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graph+216)
I/DEBUG (29934): #12 pc 0000e3a8 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graph+216)
I/DEBUG (29934): #13 pc 0000e3a8 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graph+216)
I/DEBUG (29934): #14 pc 0000e3a8 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graph+216)
I/DEBUG (29934): #15 pc 0000e3a8 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graph+216)
I/DEBUG (29934): #16 pc 0000e1f0 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (run_graphs+76)
I/DEBUG (29934): #17 pc 0000dc20 /data/app-lib/com.myapp-1/libmediastreamer_base-armeabi-v7a.so (ms_ticker_run+192)
I/DEBUG (29934): #18 pc 0000d600 /system/lib/libc.so (__thread_entry+72)
I/DEBUG (29934):
Wi-Fi to Wi-Fi call works perfectly fine.