I tried to use (mppp) channel bundling with the isdn-toolset that comes 
with RH 6.2. The Setup-Utilities do not allow to setup channel-bundling, 
but th scripts (/etc/rc.d/init.d/isdn) seem to be prepared ...

After setting the 'BUNDLING' variable in /etc/sysconfig/provider/conf-...
the system tries to setup the slave interface but accidently sets all the 
parameters for the master interface again ('device' instead of 'slave')

I fixed this part (see patch at the end) and it works fine so far.
You can use 'isdnctrl addlink ippp0' now and tools like 'ibod' also work
with it ... however, if you run isdnconfig again, it removes the BUNDLING 
variable from /etc/sysconfig/provider/conf-... again - I didn't fix this, 
but I think it should be ... :-))

I tried to supply a patch, but your server didn't accept it ...
(String too long error ...)

I'm sending it to bugzilla-owner ...