Phone number-Precautions for sending sms pdu codes to PHS

Yesterday, I spent some time solving the problem of sending text messages by GSM Modem and PHS. It was found that "+" was added by default before the phone number.
There is an address field in the PDU encoding, where there is an address type segment whose values are many ArticleIt is fixed to 0x91. In fact, this is not correct. According to the 3GPP 23040-650 description of this field, 0x91 is international, that is, add a "+" before the number. However, if the address type is fixed to 0x91 in the format of "106 + area code + number", the address type is changed to the format of "+ 106 + area code + number". The SMS center may consider it an international text message, it may be sent to another country, or it may fail to be sent.
Therefore, change 0x91 to 0x81 to solve this problem.
For ProgramTo add the "+" judgment. If the number is preceded by "+", the addresstype value is 0x91; otherwise, the value is 0x81.
For more detailed information about PDU, please refer to the 3GPP information, on my homepage: http://dream-world.nease.net on the "Information" section has PDF Version Download.