Downloading mail from a POP account into Exchange Server in general is not a supported configuration (though you wouldn't know it from the proliferation of tools to accomplish this). However, Microsoft does provide an Exchange Connector for POP3 Mailboxes for Small Business Server, having licensed Internet Mailbridge from Acotec. It's still not a supported configuration for full Exchange Server.
I'd suggest that you read about both sides of this issue. If you decide to try this route, there are plenty of tools to choose from. Features common to all POP3 collectors include the ability to POP mail from multiple servers and from multiple mailboxes. You'll also be able to control how often it checks for new mail in the POP3 accounts and limit it to downloading new mail during specific hours, such as only during business hours. All of the commercial POP3 connectors should be able to deliver mail to any SMTP address, including mail-enabled Public Folders. There are many tools available but many have poor configuration interfaces, lack statistics or clear logging or lack some essential features such as secure communications, Gmail support or genuine configurable schedules for each account being downloaded.
In order to save you time making a decision as to which tool to evaluate or purchase for your organization, we have collated the screenshots of the poor user interface design below: