So very close, but so frustrating...

[Steve <sjh_ubuntu shic co uk>]

I've a netbook and I want to use it to access my home-office email 
wherever I happen to be... with minimal fuss.  Sometimes I'll be 
connected to a wired network, sometimes wireless, sometimes via my 
mobile phone (connected over bluetooth) - sometimes from home - 
sometimes from remote locations.
To this end, I've set up a openvpn VPN using NetworkManager for my 
client which allows me to interact with my email server as if I am at 
home from wherever my netbook happens to be connected.  This works 
wonderfully well both for ethernet and 802.11 wireless connectivity.
My problem arises when I want to use my mobile phone.  I know my 
hardware works, because I can use NetworkManager to disable wireless, 
then the following wvdial configuration to establish a PPP connection... 
and - if I'm somewhere without any connectivity - it allows me to browse 
the web and make ssh connections to servers via my mobile phone.
--
[Dialer Defaults]
Init1=ATZ
Modem=/dev/rfcomm0
Baud=460800
Phone = *99#
Username = username
Password = password
New PPPD = yes
--


So far, so good... but, when NetworkManager is not aware of a network 
connection (because the mobile phone connection has been patched-through 
from the command line) it refuses to allow me to turn on my VPN.
Obviously, it would be best if I could avoid using the command line at 
all - but I'm drawing a blank on how to do this.  Under "Edit 
Connections" there's a promising looking "Mobile Broadband" - which goes 
on to give me a dialog into which I can patch the phone number "*99#" 
and username/password (though these are both ignored by the wvdial 
approach, so don't seem to be very important...) - but I can't see 
anywhere to specify the interface... /dev/rfcomm0 - which, I suspect, is 
significant.  Furthermore, even with a "Mobile Broadband" connection 
configured in "Network Connections" - I don't see how I can activate 
this from the NetworkManager GUI... (similarly for the DSL 
configurations - though those are of no practical interest to me at the 
moment...)
Is there any way that I can configure NetworkManager to allow me to 
switch between wireless connectivity and 'dialup' networking via my 
mobile phone?  It seems so close to working that it would be a shame to 
be forced back to the command line...
In case it is relevant, I'm using NetworkManager Applet 0.7.0.100 - the 
latest Ubuntu default.
Any hints much appreciated...