I've never been charged for emails. I think it depends on how your phone is set up. On my phones a N95 and a Samsung Omnia, I have an option for email.
I think possibly if your phone does not have an email function, then you can be sent emails via your text message box and that is possibly what they charge for.
You may already know how to do this, but I'll explain further below.
If you have an email option, normally in your text/picture messages section on your phone, and you have a web based email something like yahoo or hotmail etc, all you need to do, is to find out your pop and smtp settings and input them into your phones, incoming and outgoing server, just like you would if you retrieve your email through Outlook or Outlook Express.
If you have set up email through Outlook or Outlook Express, then it should be pretty easy for you to figure out. But I'll give an example below.
To recieved my Yahoo email, on my N95, I go into email settings. In the user name you need to my email username which is XXXXX (the bit before @xxxxx.co.uk), then your password in the password box. For incoming server I enter pop.mail.yahoo.co.uk (this is the incoming mail server for yahoo). The access point is the point you use for the internet, so mine is T-Mobile Internet for instance. The my mailbox name is you full email logging. The outgoing server is smtp.mail.xxxxxxx.co.uk (this is the outgoing mail server for yahoo).
I may be able to provide you with details on how to set it up on your phone, if you let me know the phone model you and email provider.
If you already know and prefer not to no problem or if you prefer to contact me off the message board via my email no problem either.