What's the difference between CRM, CMS and ERP

I know that CRM stands for Customer Relationship Management, CMS stands for Content Management System and ERP stands for Enterprise Resource Planner. I would like to know what each of things does best and which scenarios they are used in. So basic understanding of the three with differences among them and the environments in which they are used.
Edit: I read up on the Wiki a bit more and now I understand according to the ERP wiki that a CRM is a part of the ERP. My question to be more specific is:

• Why have a CRM separately if it's already a part of the ERP? Abstraction?

• To log and store the information of a call-center that calls a hundred odd people to get info, which is more better to achieve the following tasks, a CRM or an ERP? :

• Store all the information about all the people that we have been called

• Store information about which person called and how many hours a person has worked?

• Find out which employee has been more productive?

My friend strongly believes a CRM will get the job done. So thought I'd ask you guys which would be better and why does it make it better.

What is CRM?

CRM at its simplest is systems and processes for managing a company’s interactions with current and potential customers. When we talk about CRM we usually are talking about CRM Software. CRM software is used to organise, automate and synchronise sales, marketing and customer service. CRM has developed to include all areas of the customer experience, keeping the customer happy and in turn keeping them loyal and more valuable to your business. It is the process of identifying potential leads/prospects, nurturing them and guiding them through the sales process to close the business. Once they are a customer it is ensuring that you maintain that relationship and encourage repeat business – either more frequent orders or higher value.

What is ERP?

Where CRM manages the customer, ERP is used to manage the business. ERP is a system for improving the efficiency of business processes. Like CRM, ERP allows for the rapid sharing of standardised information throughout all departments. Employees all enter information into the ERP system, creating a real-time, enterprise-wide snapshot. Problems in any area will automatically create alerts in other affected areas. This allows departments to begin planning for issues before they become a problem in that department. In short, by allowing the business to focus on the data, instead of the operations, ERP provides a method for streamlining business processes across the board. Microsoft Dynamics ERP can directly integrate with Dynamics CRM.