SMS Gateway Development with SIM Box

We are in need of a professional SMS Gateway using a SIM box. The primary purpose of this SMS Gateway is to handle transactional messages. This system should also be able to integrate with our mobile apps for customer support.
Key Requirements:
- Development of an SMS gateway that can handle both inbound and outbound messages.
- Integration of the SMS gateway with our mobile apps for customer support.
- Optimisation of the system for transactional messages.

Ideal Skills:
- Proven experience in developing SMS gateways.
- Proficiency in working with SIM box technology.
- Strong skills in mobile app integration.
- Capability to handle both inbound and outbound message processing.