Follow the following instructions:
"Help! My Web Browser Doesn't Display Any Pages, Only "Loading..."!"
At the top of this document, including Configuring Internet (including filling your Options->APN setting).
See if you can go to your Nextel BWC and resending your browser service book. Call Nextel and explain you used ot have the browser on your 7510, and you want it on your 7520 too as well. If not, then you may have to keep using your Reqwireless webviewer browser.