Hi, Cally. Most things you do on your BlackBerry aside from calls and texts will use data.
From the biggest data hogs to the most efficient, in order according to my experience: Streaming music or watching videos , downloading and using apps, downloading attachments from emails, BlackBerry Messenger, push email.
If you have a newer Curve with Wi-Fi, use that as much as possible, instead of cellular data. BlackBerries compress data and don't use as much as other devices, so if you only use push email when not in a Wi-Fi area, for instance, you should be fine with 150MB unless you download lots of email attachments.
To keep track of your data usage, download the My Verizon app for your phone, call customer service (*611 from your phone) for an automated reply, look online with My Verizon, or I believe you can text too and receive a response.
Enjoy your new BlackBerry!