asterisk users - Sep 2006 - GXP2000 - Blind Transfer Hangs Up Call

I have a couple of clients with a bunch of GXP-2000. They can do  
attended transfers with no problems. However, there are times that  
the party to transfer to is simply not at their desk and the party  
wanting to transfer the call knows that. In these cases, they'd like  
to blind transfer the call so that the voicemail picks up. The  
problem is that when they do so, the call drops.

This happens in all the phones and all three clients of mine that  
have these phones.

They could leave with just attended transfer. The problem is that (at  
least on these phones), the TRFR button will not work until the party  
picks up and not while it's ringing. So, currently, they need to let  
the phone ring until the voicemail picks up before they can transfer  
the call.

Is there a "trick" to blind transfer a call on these phones (or in  
general)?

Thanks,
Daniel