I almost posted this as an "Ask HN". I need to find a way make calls over the cellular networks of the major USA carriers. That is, I need to exactly simulate s

I almost posted this as an "Ask HN". I need to find a way make calls over the cellular networks of the major USA carriers. That is, I need to exactly simulate sending a request through their network to a website. I've been looking, but I've been unable to find information about what these companies offer, in terms of testing sandboxes. Does anyone know what these companies offer?