The Blackberry support true push email using BIS (Blackberry Internet Services) you can setup email accounts (like your Gmail account) and it get pushed to your Blackberry - there is a lot of detail on how this works but I will not explain it here.
As in previous blog entry you can pay R59 per month (30 days) from your Vodacom airtime which give you unlimited internet access on your Blackberry meaning that you don't pay R2 per 1 MB for internet (3G/GPRS/EDGE) - push email, Facebook and browsing is free.
There are limits, you can't for example download huge emails, emails got a limit size as well etc. I suggest you check with your service provider (Vodacom, MTN) onthese limitations.
Also at work my phone is always on silent, the Blackberry got it nice where if there's a email a little red light flickers - very nice visible notification.