Trouble Ticket Management For Client Support Service Providers.

Our organization is looking for a robust, open source trouble ticket management software for our client support based computer service business.

We provide technical support, web hosting services and do a wide variety of network/computer service for hospitals and also some small to medium sized business.

We receive many email and phone support requests and need a reliable way of tracking and managing their priority and results. So we need something that can accept tickets or support requests by email.

Have you any suggestions on any software? Open Source is preferred since it just makes sense nowadays. We can run on any linux/windows os and platforms, web based is welcomed.