MOT call/sms problem

Hi,all: I have got a C118 to test mobile function 1) To get the master branch code and to compile it. 2) To insert simcard(13681******) into the phone and to modify the mobile.cfg to use real simcard. 3) To connect the phone with PC(core i5/ubuntu 12.04). 4) After downloading the firmware, to start the mobile App(#sudo ./mobile 2>&1 | tee > log.txt). 5) I can see that the location update process is ok and an TMSI is allocated to the phone. 6) To telnet into the osmocon, I can start a call to another phone (#Call 1 13564******). 7) I can send a sms to another phone. So far, all(MOC) is ok. But If using the osmocommbb phone(13681******) as the target phone(MOT), (for example, Iuse a normal phone to call the osmocombb phone), it is very rare that the osmocombb phone have a respose to the paging. 1) I have check the paging messages in the log.txt file and find that there only one paging respone messages such as "TMSI MATCH" as I have call the osmocombb phone about 20 times. In the success case: ..............gsm322.c:1966 Cell ARFCN 13 selected.gsm322.c:2423 Tune to frequency 13.gsm322.c:468 Sync to ARFCN=13 rxlev=-68 (Sysinfo, ccch mode NON-COMB)gsm322.c:2450 Cell available.gsm322.c:4049 (ms 1) Event 'EVENT_CELL_FOUND' for Cell selection in state 'C5 choose cell'gsm322.c:3383 Camping normally on cell (ARFCN=13 mcc=460 mnc=00 China, China Mobile)gsm322.c:829 new state 'C5 choose cell' -> 'C3 camped normally'gsm48_mm.c:4325 (ms 1) Received 'MM_EVENT_CELL_SELECTED' event in state wait for network commandgsm48_mm.c:1130 We are in registered LAI as returning to MM IDLEgsm48_mm.c:919 new state wait for network command -> MM IDLE, normal servicegsm48_mm.c:426 starting T3212 (periodic loc. upd. delay) with 7200 secondsgsm322.c:2947 Channel synched. (ARFCN=13, snr=16, BSIC=29).............. gsm48_rr.c:2116 TMSI a0b186e9 matchesgsm48_rr.c:1307 Establish radio link due to paging requestgsm322.c:4049 (ms 1) Event 'EVENT_LEAVE_IDLE' for Cell selection in state 'C3 camped normally'gsm322.c:829 new state 'C3 camped normally' -> 'connected mode 1'gsm322.c:3665 Going to camping (normal) ARFCN 13.gsm322.c:468 Sync to ARFCN=13 rxlev=-68 (Sysinfo, ccch mode NON-COMB)gsm48_rr.c:355 new state idle -> connection pendinggsm48_rr.c:1422 CHANNEL REQUEST: 20 (PAGING TCH/F)gsm322.c:2947 Channel synched. (ARFCN=13, snr=16, BSIC=29) .......... From the log info I can see that: a) the phone is camped in ARFCN 13 and receive paging in this cell. b) the signal of cell is strong enough 2) I have no an OpenBTS device to send some paging messages to check where is the problem further. Maybe I miss something. Any suggestion is appreciated! Thank you very much! Best Regards Shang