On July 2 2011, there will be no more support in the form of Service packs, Maintenance Release or Security vulnrabilities. You will however be able to call in and get support to fix it if need be.
This might be a good time to think about an upgrade to BES 5 or BES 5 Express.
You can compare features here.
http://us.blackberry.com/apps-software/business/server/express/ComparisonChart_NA_021610_v3.pdf
To migrate to BES 5
Since BES 5.0 is so different, I would set it up all on its own and once tested and running, use transporter to move users over which will not require any activation. You can also get a migration kit from T support for this so you can have both new and old running at same time. Other otion is use BES express as middle man to move to and then once all moved, move to Full BES. (migration kit is alot easier)
Here is most of the documentation you need will to install and administer the BB 5.0 server:
Server 5.0 Upgrade Paths:
http://na.blackberry.com/eng/services/server/upgradepath.jsp
Server 5.0 Intsallation Support:
http://na.blackberry.com/eng/support/software/serverinstall.jsp
Server 5.0 Upgarde guide:
http://docs.blackberry.com/en/admin/deliverables/7315/index.jsp?name=BlackBerry%20Enterprise%20Serve...=
BlackBerry Enterprise Server Resource Kit Docs and Files
https://www.blackberry.com/Downloads/entry.do?code=D736BB10D83A904AEFC1D6CE93DC54B8
http://docs.blackberry.com/en/admin/subcategories/?userType=2&category=BlackBerry%20Enterprise%20Ser...
Server 5.0 Admin Tutorial:
http://docs.blackberry.com/en/admin/deliverables/7466/flash_start.html
All Server guides:
http://docs.blackberry.com/en/admin/?userType=2
BES 5 Express you can use this thread for upgrading stratagies.
BES/SBE/BPS 4.x upgrade options to BES Express 5.0
And for those going to Exchange 2010, please follow this after you upgrade to BES 5.
How to migrate the BlackBerry Enterprise Server 5.0 from Microsoft Exchange Server 2003 or 2007 to M...
