"I tried the above method, but the APM Planner could not connect to my drone.

My computer connects to the internet through a DSL Modem (Router). Therefore I don't have a direct public IP Address but only an internal IP. Could this be a problem? "

"hey Andreas, great work!

I also have a SIM900 Shield and want to try 3G Telemetry with it. I have followed the instructions given here, 
http://diydrones.com/group/telemetry-over-cellular-ip/page/testing-...

but couldn't figure out step 6, where…"