frame addr usage

[Bob Weber]

The gdb documentation lists the ability to access a frame by it's address
frame addr

Can anyone tell me how to use this command?  
Does it work on the x86 platform?
Is there special syntax required?

If I type the 
info frame

I get 
 
(gdb) info frame
Stack level 14, frame at 0xbfeff568:
 eip = 0x40127db9 in task_internals::allocate(unsigned) (file.cxx:134); saved eip 0x40127db9
 called by frame at 0xbfeff728, caller of frame at 0xbfeff3a8
 source language c++.
 Arglist at 0xbfeff568, args: this=0xbffff490, requested_stack_size=1056768
 Locals at 0xbfeff568, Previous frame's sp in esp
 Saved registers:
  ebp at 0xbfeff568, eip at 0xbfeff56c

I would think I could reference the previous from with  the address 0xbfeff728 like so

(gdb) frame 0xbfeff728

But this is the result returned

#0  0x00000000 in ?? ()

Can anyone out there help?

Thanks,

Bob