This is not as simple as it seems at first glance.
I was working on a project in the Middle East some time ago, when we had this exact requirement, and we really had to enlist the support of a local telecommunications company to support our efforts.
In fact, it all depends on how the SMS works.
Most people think that SMS is sent in byte orientation over an 8-bit channel, just like MMS and GPRS data, but in reality it is not.
SMS is actually sent to the signaling channel of most GSM-based devices (therefore, your SMS does not work when the phone rings, for example)
In addition, only a small portion of this signaling channel is used, and often this occurs outside the serial data band.
Given this information, at least you need a local GSM connection that could be addressed using standard msisdn (i.e. the real name for the phone number), then this connection would have to provide a standard C7 signaling environment that can respond to and serial data decoded before it is redirected to a server based on SMPP (or similar) at the end of the connection.
Once you had the decoded message on the server and you analyzed the various flags in the PDU so that the message knew that it was a USSD message, then you would need to remove the message from the queue, process it, find out what this command meant, and then send it to the application server, which will then determine which URL to call, or which soap endpoint to transmit, and many other factors, as well as accept any response, converting it back to SMPP, then serializing it again and sending it back to the signal channel l to the original device.
Now, with the right know-how and equipment, you can certainly customize your own. Many mobile phone providers these days will provide their customers with pico cells in poor coverage areas, and you can also buy stubs that can be connected to a local PC, but you must be absolutely sure that you are allowed to do this in your area.
Many authorities strictly control which radio resources are not allowed in any particular area, and heavy fines or imprisonment will be the result of those who violate these laws.
Once you have the antenna, you can run something like "Open BTS" on the machine to which the antenna is connected. Open BTS does everything that standard GSM BTS software does, including transferring data upstream from aBis to things like the SMPP servers used for SMS traffic.
However, it does not provide SMS software, for this you will need another computer with a standard Linux distribution on it, and then software such as configuring and starting Kannel, when you have a channel, then you have the ability to process messages.
Do it all together and you can conduct local USSD testing.
there is a much simpler alternative, but it will probably cost you a little money, and to register with a service provider such as the global USSD ( Link Here ) or similar, who for a fixed fee will do all the hard work for you, leaving you focused on the answer to your calls to the application.