Id say no as "Fire for Effect" is a special order that the command squad issues in the command phase to any unit with the Artillery Strike ability and does not contradict or replace the Radioman ability. You would also have to use the Radioman abiltity to issue the order to an observer squad outside of command radius.

PG 88 "Once per Command phase, the platoon’s Command Section may issue a “Fire for Effect!” Order to one unit with the Artillery Strike ability (which may include itself). The unit receives a Reaction Marker. Then roll a single Combat Die, and on a hit the ordered unit may resolve a 220mm Long Tom attack against up to two target units. Each target unit must be within 6” of each other. The attack may fire indirectly, even though the unit did not take a Sustained Attack action."

In order to stop the Long toms you would either need to wipe out the command squad or kill all the Radiomen in the force (within command radius).

 Fire for Effect is a special order given by the platoons commander in the Command Phase and so would follow exactly the same rules as every other command order in that it can only issue orders over 12" one per radioman, and being off table the Long Toms would be over 12" away.

Major Mishap said:

You're issuing the command to a radioman on the board not off board…

the ranger command squad could
 1. issue the command to itself as long as its own radioman is alive (he has the art-strike). The ranger command receive a reaction marker per the rule.
 2. issue the command to another unit with a radio man within 12" - that receiving unit then gets a reaction marker. The ranger command squad is then free to use it's own radioman as normal.
3. issue the command to another unit outside of 12" - that receiving unit gets a reaction marker. The ranger command squad would have used it's own radioman to issue the order.

that's my take on it anyways

 True, just issue the order to a unit with a radioman as per normal orders.

 but the radioman isn't carrying the long tom around in his backpack, he's gotta call it in and give firing coordinates…  does that mean you also use that same radioman to relay another order to an out range unit during the same command phase?  i still feel like the rules dont touch on this explicitly, so maybe it comes diwn to interpretation…

speaking of radiomen…  is it only the radioman in the command squad that allows an extra-range order?  if you have an observer squad on the table with two radiomen does that allow two additional extra-range orders?  or is that only if they're with a hero that's serving as the command section?

 Nothing in the rules saying you can't use the radioman twice, he doesn't even use up any of his actions.  Only radiomen in the command section can issue long range orders.

calvinc71 said:

The command squad has the ability to issue an order to a radioman to call in the long tom attack… the command squad isn't calling in the attack itself.

If the command squad gives the order to it's own radioman then it receives the reaction marker and rolls the die.

If the command squad gives the order to some observers close by then the radioman in the command squad only comes into play if the observers are more than 12" away. At which point the observer team gets a reaction as it calls in the long tom attack.