不插SIM卡，不能拨打紧急电话

[DESCRIPTION]
不插SIM卡，手机不能拨打紧急电话

Root Cause

手机没有写入合法的IMEI；或者当地的某个运营商不支持紧急电话，而手机正好选上了这个运营商；或者当地的某个运营商不支持无SIM卡的紧急电话，而手机正好选上了这个运营商
[SOLUTION]
检查手机是否有写入合法的IMEI
用对比机切换到同一制式（与测试机同为2G或者同为3G），同样不插卡看对比机是否能拨打，
Note: 由于不插卡情况下手机会忽略运营商而只按照信号强度选择小区，不同的手机由于硬件差异可能选择上不同的小区，所以在拿做对比测试的时候，可以多换几个地点来测，在每个地点都重新开关机再试。另外可以通过察看log中消息MSG_ID_MMI_NW_ATTACH_IND来知道手机连接到的网络。
Example
 深圳移动2G支持紧急电话，联通2G不支持拨打紧急电话，手机不插卡情况下在有些地区会选择上移动小区就能打紧急电话，在另一些地区会选择上联通小区就不能打紧急电话。

 

 

从代码层面上分析如下：

 

无卡时拨打紧急电话失败原因可能有三：
1.    当网络发送回来的reject cause为CM_MM_INVALID_MM_MAND_INFO或CM_MM_IMEI_NOT_ACCEPTED等cause时，与IMEI有关；无卡情况下拨打紧急电话时，需要IMEI来给网络鉴权，如果网络判断IMEI非法，会reject；
2.    当网络发送回来的reject cause为2173 即CM_MM_EMERGENCY_NOT_ALLOWED或
3175 即CM_MM_ACCESS_CLASS_BARRED等cause时; 与手机当时连接的cell有关：
3.    在没有插SIM卡时，手机根据当前网络信号强度来注册，如果联通网信号比较强，手机注册的是联通网，而联通网不支持拨打112，所以无法拨通； 如果移动网信号强，则注册移动网，则可以拨通112；可以通过察看消息MSG_ID_MMI_NW_ATTACH_IND来知道手机连接到的网络, 中国移动: 46000, 中国联通: 46001。
    第1点GSM 04.08 中的4.5.15节的说明：
If the network does not accept the emergency call request, e.g., because IMEI was used as identification and this capability is not supported by the network, the network will reject the request by returning a CM SERVICE REJECT message to the Mobile Station.
Normally, the mobile station will be identified by an IMSI or a TMSI. However, if none of these identifiers is available in the mobile station, then the mobile station shall use the IMEI for identification purposes. The network may in that case reject the request by returning a CM SERVICE REJECT message with reject cause:
#5 "IMEI not accepted".
    第2点GSM 02.11中4.4节的说明：
 An additional control bit known as "Access Class 10" is also signalled over the air interface to the MS. This indicates whether or not network access for Emergency Calls is allowed for MSs with access classes 0 to 9 or without an IMSI. For MSs with access classes 11 to 15, Emergency Calls are not allowed if both "Access class 10" and the relevant Access Class (11 to 15) are barred (GSM 04.08 [6] refers). Otherwise, Emergency Calls are allowed.