VOIP IVR System Needed

We need VOIP based IVR system. We need IVR system hosted on cloud with custom IVR options based on the Called ID. Below is the basic flow: 1. Customer calls to our Customer Care 2. Our Cloud Hosted IVR will receive the inbound call and start to play a Greeting Message 3. In the mean time while playing the Greeting message, the system will consume the Restful API exposed from our CRM. 4. In the API it will pass the caller number and our system will return the Welcome message to be played and the IVR menu options to be provided to the caller. 5. Please note that the IVR menu options will be different and dynamically generated based on the caller ID. So our API will either return the dynamic options in text form and the IVR system will convert from text to audio. Or our API can also return the IVR Menu ID, based on IVR menu ID, the IVR system will play that specific IVR to the caller. What we need: 1. The cheap and best Cloud IVR hosting. We are based in India 2. There should be provision to modify the IVR design code 3. The pricing plan should be - Pay per call. 4. Our monthly inbound calls will be approx 500 to 1000 calls per month