This is what my mums phone did.
Go on the main menu, click 'options' then 'advanced options' then 'applications' then wait for the applications to load up and find 'blackberry app world'
click on it, press delete
then go on your main phone browser or preferably 'google', type in 'download blackberry app world' and so on from there and then if it asks for a reboot, allow it.. then do a batt-pull and it should work
also, if it doesn't download then once you've deleted it from 'options' > 'advanced options' > 'applications' then you should have the blackberry app world icon on your main menu, click on that and 're-install' and it should work perfectly fine.
If you still find that once youve done all of this that it still freezes then..
click 'alt' then 'l' then 'alt' then 'g' then 'alt' then 'l' then 'alt' then 'g'
so your repeating the same procedure twice, a list of stuff should come up, click your 'blackberry dots' on your handset and click 'delete' this should stop the phone from freezing, i do that procedure almost everyday to stop my phone from freezing and i've not had any problems.
HOPE THIS HELPS,