Required VoIP freelancer for SMS solution via SIM routes and/or grey routes job

We are interested in developing a solution for sending SMS messages via the SIM routes. I heard different options. I'd like to hire someone to come up with a feasible solution. This is usually used for sending bulk SMS messages (for marketing).

If you are familiar with the model - you can suggest hardware, software etc.

I prefer to see a working solution for bulk SMS messaging that you are currently using.

Skills & Expertise Required

VoIP