Can I use my SIM900 GSM module to store AT commands via puTTy hyperterminal? I mean to say that will the module follow the command after plugging it to power which was sent before plugging it?
Some modems support scripting languages, like Python, which can be run automatically at start up. This kind of stuff is usually described in the product documentation, and support materials. There should be a class of configuration settings that can be written to one, or more, configuration profiles.
Other than those types of thing, you'd actually need a micro-controller to set up and establish the connection.