The open source Android client can be used to send authorization packets to a server running fwknop, thus opening ports based on a predefined ruleset. The application also has the ability to launch ‘Connectbot’ and connect to SSH, if this is the port being opened. Note that at the moment the Android client only provides only the most basic options of fwknop, and lacks GPG functionality, but hopefully we can look forward to these being added in the future.
Using a phone-based client to send an authorization packet on behalf of another computer can actually improve the security somewhat, as you’re sending that packet out-of-band (OOB), making it less susceptible to interception if the computer’s network traffic is being monitored.
Now we just need an iPhone/iOS app! Come on developers.