This is more of a what if than anything else and probably should not be here. We know that Germany and Japan in WW2 never was a looking at each others as allies since both sides did not talk to each other about there plans like the invade of the USSR, or the bombing of Pearl Harbor and such. How would the war change if they did talk these plans over to each other informing the other side as to what could work best? Would the war be about the same as we know it or would it be more costly in term of human lives. I know that both the Japanese and Hilter wanted to built their own "Empire" as to speak.
The origination of the alliance between Germany and Japan was in the form of the Anti-Comintern (Communist International) pact. Namely, both nations signed the treaty in response to the Soviet Union.
However, in 1939, Germany signed the Molotov-Ribbentrop pact with the Soviets. Combined with German assistance in arming the Nationalist Chinese (whom were engaged in a bloody war with Japan), the Japanese saw this as a stab in the back. The Germans attempted to mollify this by the signing of the Tripartite agreement, but German-Japanese collaboration was minor at best, in no small part due to the fact that the only connections between Germany and Japan were by sea (which the British navy dominated) and the Trans-Siberian railroad (which became moot after Operation Barbarossa).
Even if there was some sort of magical space radio that allowed the German high command and the Japanese high command to talk, it is extremely unlikely that they would attempt to launch collaborative campaigns. Germany's intended decisive campaign was against the Soviets... which the Japanese had signed a non-aggression pact with to protect their interests in Manchuria and Korea, and had no intention of breaking. Similarly, Germany had no real way to provide any support to Japan, as its navy was too small to act as anything other than surface raiders or as a submarine threat.
There some more information in the AskHistorians FAQ right here:
http://www.reddit.com/r/AskHistorians/wiki/wwii#wiki_axis_alliance_and_post-war_plans