Deploying a BES server for anything below 500 users and/or below top secret information is pointless. The charges and administration fees are high.

What you could do is a "hybrid" solution on a budget. I am using Orange's BIS Blackberry service and use a private and a business email on it.

The private mail is a gmail, nothing much to talk about.

If you know your business pop3/imap/smtp information, this is a no brainer. If your company however is tough on allowing access from outside through the aforementioned, here is how I went around it.

My business email is setup to forward copy of each received email to a second gmail. Now, inside gmail you have an option to "send email as" - dig through the settings. Basically, you enter the email that you wish to appear as sender, then gmail generates a confirmation email to this same account. Once you reply to this confirmation, in gmail you will be able to pick from which identity to reply.

In short, on a single blackberry phone, with BIS you can have up to 10 email accounts set. I use only two - one personal and one business, without need for BES and with the ability to respond as employee@company.com from the device.

I hope this info is useful for you - do not hesitate to ask if my tips miss a piece you need.