Didn't understand the quite clearly? for what application this is going to get used? please explain
There are two ways. If numbers are fixed that is if there are say 10 numbers then you can store them in eeprom or ROM and then when SMS has to be sent then read one number from memory and build the AT+CMGS+"number" command and send the SMS. If numbers can change then use a keypad to key in the mobile numbers like the device asks enter no. 1 and you enter mobile no. 1 and it sends SMS to that number. You can also have different SMS for different numbers. Based on the no. being entered that is 1, 2, 3,... different SMS is read from memory and sent. Alternately youy can use a SD Card and store the mobile numbers and messages in it. Read SD Card and send SMS.