I have tested today with Cinterion MC75i modul http://www.cinterion.com/mc75i.html (USRP still with internal 64MHz clock).

intialization & info:
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ati
SIEMENS
MC75
REVISION 04.001

OK

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monitoring, modul was camped on openbts without SIM, Limited Service means only emergency calls are available
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at^moni
Serving Cell                                          I Dedicated channel
chann rs  dBm MCC MNC  LAC cell NCC BCC PWR RXLev  C1 I chann TS timAdv PWR  dBm Q ChMod
   29 67  -43 001  01 029B 000A   0   0  39  -111  61 I    Limited Service

OK

at^moni
Serving Cell                                          I Dedicated channel
chann rs  dBm MCC MNC  LAC cell NCC BCC PWR RXLev  C1 I chann TS timAdv PWR  dBm Q ChMod
   29 63  -47 001  01 029B 000A   0   0  39  -111  57 I    Limited Service

OK
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I requested to scan other BTS from the operator, but there is only one USRP
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at^monp
chann rs  dBm MCC MNC BCC  C1  C2

OK
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I requested to display all operators, but it probably cannot work without SIM
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at+cops=?
ERROR
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I have inserted expired testing SIM and restarted
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^SYSSTART
ati
SIEMENS
MC75
REVISION 04.001

OK
------------------------
modem camped to openbts, No connection means full service, no active call is proceeding
------------------------
at^moni
Serving Cell                                          I Dedicated channel
chann rs  dBm MCC MNC  LAC cell NCC BCC PWR RXLev  C1 I chann TS timAdv PWR  dBm Q ChMod
   29 63  -47 001  01 029B 000A   0   0  39  -111  57 I    No connection

OK
at^moni
Serving Cell                                          I Dedicated channel
chann rs  dBm MCC MNC  LAC cell NCC BCC PWR RXLev  C1 I chann TS timAdv PWR  dBm Q ChMod
   29 63  -47 001  01 029B 000A   0   0  39  -111  57 I    No connection

OK
------------------------
still have only one openbts
------------------------
at^monp
chann rs  dBm MCC MNC BCC  C1  C2

OK
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request to display all operators, (230 is country code of Czech rep.)
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at+cops=?
+COPS: (2,"CC 001 NC 01",,"00101"),(3,"EUROTEL - CZ",,"23002"),(3,"T-Mobile CZ",,"23001"),,(0-4),(0,2)

OK
at+cops=?
+COPS: (2,"CC 001 NC 01",,"00101"),(3,"T-Mobile CZ",,"23001"),(3,"EUROTEL - CZ",,"23002"),,(0-4),(0,2)

OK
------------------------
request to display all operators, this command is almost same only displays another name (Rudy is set on OpenBTS)
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at^sops=?
^SOPS: (2,3,"Rudy","","00101"),(3,4,"TMO CZ","","23001"),(3,4,"ET - CZ","","23002"),,(),()

OK
------------------------
request to connect on T-Mobile
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at+cops=1,2,23001
OK
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expired SIM, no full service
------------------------
at^moni
Serving Cell                                          I Dedicated channel
chann rs  dBm MCC MNC  LAC cell NCC BCC PWR RXLev  C1 I chann TS timAdv PWR  dBm Q ChMod
   55 41  -69 230  01 401E 061F   3   0  33  -106  36 I    Limited Service

OK
------------------------
request to scan other BTS from the operator
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at^monp
chann rs  dBm MCC MNC BCC  C1  C2
   59 26  -84 230  01   3  21  21
   33 24  -86 230  01   4  19  19
   35 24  -86 230  01   3  19  19
  104 19  -91 230  01   3  14  14

OK
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 request to display all operators while camped on T-Mobile
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at+cops=?
+COPS: (1,"Vodafone CZ",,"23003"),(1,"CC 001 NC 01",,"00101"),(3,"T-Mobile CZ",,"23001"),(3,"EUROTEL - CZ",,"23002"),,(0-4),(0,2)

OK

at^sops=?
^SOPS: (1,2,"Oskar","","23003"),(1,3,"Rudy","","00101"),(3,4,"TMO CZ","","23001"),(3,4,"ET - CZ","","23002"),,(),()

OK