looking for web based software to take emails from a call centre and manage case

Hello
SItuation: engineers on call out to fix faults.
We have a 24/7 fault reporting number run by a call centre. It fwds calls to the relevant engineer and sends an email to an email address at our company. We need to have a help desk type of software (web based and hosted) which can take these emails, acknowledge to customer with a ticket number and to engineer. Want engineers to be able to update the case from a Blackberty, solve it, and there to be a knowledge base elemengt, escalation etc. Low call volume - 70 calls a week. All info welcome!