You’ll need to contact your Exchange admin to get the new URL for your companies Webmail. They will also need to reconfigure the Blackberry Enterprise Server to point your phone to your new mailbox on the Exchange 2007 server.
The question was regarding BIS, not BES, so there is no need to reconfigure anything on the BES, there isn’t one for this user. Accessing OWA through BIS will work as long as the exchange admin has not blocked BIS access to the exchange OWA web site. So yes, get the new url, typically for exchange 2007 you do not need to include /exchange on the end. Our Exchange 2007 url is https://webmail.companyname.org. You may need to ask if the site is blocked to BIS users. This is a security measure exchange admins will take to block personally owned unauthorized devices from accessing exchange. You may need to find out if there is a policy regarding personal devices enacted as well.