security is pointless in this case i think. everybody on the local side should be able to dial-up, it's impossible if you're not already dialed up for someone from the outside to tell it to dail-up....

untested, but i would probably just try something like:

# /etc/services
dialup   12345/tcp     # dialup
dialdown 12346/tcp     # dialdown

# /etc/inetd.conf
dialup stream tcp nowait username /etc/init.d/dialup start
dialdown stream tcp nowait username /etc/init.d/dialup stop
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then if you add the services to the client machines you can just 'telnet server dialup' to start the connection and 'telnet server dialdown' to stop it.

for more perlish solution look at Net::Server or maybe the RPC or SOAP

it's also likely that you could configure the dialup server to automagically dial on demand. and not have to bother with anything else.