4) Download alternative software
a) It is pretty obvious that since you aren't subscribing to BlackBerry's Internet service, you won't be able to use push e-mail on your phone. Also, you won't be able to use the built-in mail client for downloading any e-mails. If you use Gmail, then you need not worry since there's a dedicated Gmail app that works on regular GPRS. But what about your office e-mail ID? Here's a workaround
Link your official mail to your Gmail account. Simply log into your Gmail, on the top-right corner, click Settings -> Accounts and Import -> Add POP3 account. Type in your official e-mail ID followed by the password. Next, it will ask you to enter POP settings.
If you aren't aware of these details, ask your system admin at the office for information. If you want to keep work and personal e-mails completely separate, then just create another Gmail account and follow the steps from before; since the Gmail app supports handling of multiple Gmail accounts.
Now, all e-mails from your official mail ID should get downloaded onto Gmail at regular intervals, which, in turn, will be viewable via the Gmail app on your BlackBerry. The app is pretty easy-to-use and has all the basic features of Gmail like the awesome search engine, threaded conversations etc. It also blinks that LED next to the ear-piece indicating new e-mails.
Alternatively, you can also look at Logic Mail, a 3rd party SMTP/POP e-mail client app. All these workarounds may not be as prompt as push e-mail, but then if you don't mind receiving mails with a little delay, then this would suffice.
b) Next, certain pre-installed apps made especially for BlackBerry will not work with the GPRS settings that we've just keyed in. Apps like Google Talk, Yahoo/MSN messenger, BlackBerry Instant Messenger, Twitter and Facebook will not work as they need BlackBerry's Internet service to be activated. So, we'll need to install alternative apps. For Google Talk/MSN/Yahoo Messengers, install an app called Nimbuzz. It is a multi-protocol chat client supporting all the former mentioned chat services along with Facebook Chat, AIM, Skype and ICQ too. Unfortunately, you won't be able to communicate with your BlackBerry Messenger pals without its service; no workaround for that one the best of my knowledge.
c) The built-in browser mostly works, but its not one of the best to surf full-fledged websites. So, its always a good idea to have Opera Mini installed alongside.
d) For Twitter, the Seesmic app works fine without the Blackberry Internet Service. For Facebook, you could rely on m.facebook.com
e) Lastly, the Google Maps application works fine over regular GPRS Internet, at least in newer handsets from the Curve, Bold or the Storm series.