Greetings,
Hope we could work on this.
I have the experience to complete this project. I recently finished an USSD integration in Kenya. The integration was not to mobicents gateway, but USSD is a standard specification,so integrating to mobicents should be no problem.
I have found online a manual for the mobicents USSD platform,currently having a look at it.
If you would love to see my work first on USSD before deciding whether am the right guy for the job,that's fine. Just let me know in chat, and I will organize for that.
Looking forward to hearing from you.