PlaySMS is a free and open source SMS management software. From the site:
"A flexible Web-based mobile portal system that it can be made to fit to various services such as an SMS gateway, bulk SMS provider, personal messaging system, corporate and group communication tools"
It currently supports more than 10 different gateways, several of which are REST API based. We would like to build an additional gateway plugin for another, currently unsupported, REST API based provider. The currently twilio gateway plugin is proof that it is possible, and with some changes can probably be adapted to the purpose.
Please inquire for details.