Have you gotten the GSM module to work 'out of the box' with any of the stock examples?
Put any/all bluetooth stuff aside for now... and ensure you have a working GSM/SIM 900 module.
Lets take a step back here for a second.
1.) You have '6' BT modules... right?
- connected to what?
- have you ensured these are working at all? (have you been able to receive any BT (serial) data on an end deivce?) (ie: your andriod cell phone perhaps? to check if you are even sedning data properly?
2.) You have this SIM900/GSM module... connected to what?
In general terms.. you need to have your Arduino with BT modules connected (although if you have 6 connected to the same Arduino..... I'm failing to grasp WHY? instead of just using one?) If these BT modules are each connected to its own Arduino and are placed around an specific area, that makes more send.. but not 6 connected to 1 Arduino board?
The arduino will check some sort of event (temp/sensor value) and then use the BT module to send this serial data out THROUGH the sedning BT module..
over to another BT module connected to its OWN Arduino... where it will receive this serial data from BT/Arduino set#1.. and parse it.. based on the data received, it will then send some AT commands to the GSM/SIM 900 connected shield to TEXT you.
So in a trimmed/paired down project scenario..
BT module connected to Arduino (for sending your 'data')
BT module connected to Arduino that has the SIM900/GSM shield attached (for receiving your data from the above BT/Arduino pair)... and in turn will send a TEXT to your phone.