в гугле с полпинка находится
например неплохо вот тут описано - раздел ERRORS
http://www.gsmfavorites.it/support/xmstoolkit/?kb=Q4801512Q4801512: In the Log File, I noticed: '+CMS ERROR: 512'. What does it mean?
A: CMS ERROR: 512 indicate 'MM establishment failure'. This error occurs when you try to send a message and the module is receiving another one at the same time. This causes a collision in the message transfer protocol resulting in failure in sending the SMS and hence, +CMS ERROR: 512. Sometimes, +CMS ERROR: 512 may also occur when the module is receiving weak signal and is loosing connection.
это из общедоступного.
Согласно GSM 07.05 ошибка 512 обрабатывается на усмотрение производителя,
но по негласному соглашению, большинство индицирует ею коллизию сообщений.
Вот может пригодится по кодам ошибок
ETSI GSM 07.05 version 5.5.0
3.2.5 Message Service Failure Result Code +CMS ERROR
Final result code +CMS ERROR: <err> indicates an error related to mobile equipment or network. The
operation is similar to ERROR result code. None of the following commands in the same command line is
executed. Neither ERROR nor OK result code shall be returned. ERROR is returned normally when error is
related to syntax or invalid parameters.
Defined Values
<err> values used by common messaging commands:
0...127 GSM 04.11 Annex E-2 values
128...255 GSM 03.40 subclause 9.2.3.22 values
300 ME failure
301 SMS service of ME reserved
302 operation not allowed
303 operation not supported
304 invalid PDU mode parameter
305 invalid text mode parameter
310 SIM not inserted
311 SIM PIN required
312 PH-SIM PIN required
313 SIM failure
314 SIM busy
315 SIM wrong
316 SIM PUK required
317 SIM PIN2 required
318 SIM PUK2 required
320 memory failure
321 invalid memory index
322 memory full
330 SMSC address unknown
331 no network service
332 network timeout
340 no +CNMA acknowledgement expected
500 unknown error
...511 other values in range 256...511 are reserved
512... manufacturer specific