I have a technicolor TG587n v3 and cannot connect to anyone that seems to be running a small private server. I can connect to the larger hosted servers without any problem.

Have tried port forwarding without any success...

*******FIXED********
Okay - I've managed to get it working... The things I did:

• I gave my pc a public IP Address within the modem settings.
• I'd already added the telnet commands that people have referenced elsewhere using the Arma ports
• I changed my steam game settings to use the latest development build under the Beta tab (right click on the Arma 3 game and select (I think) Game Properties - the bottom option...)

I'd also port forwarded and added that to my game applications within the modem but I don't think that was the thing that made a difference.

So, one, some or all of those things now allows me to connect to all servers, not just (what looked like) the larger dedicated ones :)