How can I add phonebook entry to sim card using Arduino GSM shield?
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Hope this helps.  

Go check out (http://m2msupport.net/m2msupport/sim-phonebook-at-commands/) I use these commands on my AI Tinker A7 board for the Arduino.... 95% work perfectly...

Cheers,
Capt.K

ps. I made these numbers up but the formats are all correct.

//----------------------------------------------------------
//---Add Entry To PhoneBook:
//----------------------------------------------------------

AT+CPBW=1, "+61416199234",145, "Paul"    //-- add entry x1

OK

//----------------------------------------------------------
//--DELETE phonebook entry:
//----------------------------------------------------------

AT+CPBW=1  //-- delete entry x1

OK

//----------------------------------------------------------
//-- AT+CPBW=[&lt;index&gt;],&lt;number&gt; [ ,&lt;type&gt; [,&lt;text&gt;]]
//----------------------------------------------------------
//
//&lt;index&gt;   = Entry Number in SIM Memory
//&lt;number&gt;  = "The Phone number"
//&lt;type&gt;    = "The Phone Number" (TYPE ) ie. 129,161,145,177.. 
              //  129 – National number type
              //  161 – National number type
              //  145 – INternational number type
              //  177 – Network specific number
//&lt;text&gt;    = "Person Name" etc.

//----------------------------------------------------------
//  Add 4x new entries to the SIM card
//----------------------------------------------------------
AT+CPBW=1, "+61416199234",145, "Pops"
AT+CPBW=2, "+61420921234",145, "Mum"
AT+CPBW=3, "+61733728171",145, "Wendy"
AT+CPBW=4, "+61356821234",145, "Mr Smith" 

//NOTE:  In Australia (above examples) the actual phone numbers
//       above are of these types
//
// Int.Format    Aust. Dial Internal       Phone_Type
// ----------------------------------------------------------- 
// +61416199234  (0416) 199 234             Mobile/Cell
// +61420921234  (0420) 921 234             Mobile/Cell
// +61356821234  (03)   5682 1234           Landline/PSTN