[Imp]

Okay lets clarify
White is solid contact so I think of voice not radio as it often is but you dont realy need to know.
Yellow is radio only

Radio contact is OK, but the link is not 100% reliable!

It can lose contact as short range radios do.
Modern times this wont happen to often old systems its more common.
This is coded in a 1950s radio is not as good as a 2000 radio plus the country.
USAs radio is probably more reliable than Chinas in 1950 for example plus more units will probably have them.
From the GG

This leader provides rally opportunities
for his subordinates but when 'command' is set to on in the preferences (and only absolute beginners turn this reality setting off!) then he must be

in contact

with his subordinate in order to command him. For units with a radio, this can be anywhere on the map. Provided the radio is working

at that point in time. All radios have a chance not to be in contact, and so are never as reliable as voice range communications.

In game terms this noticably makes modern formations more flexible as they can spread out & still stay in contact more easily.

While I am at it more stuff from the GG.

2) Previously radios were given to almost every platoon leader and section leader no matter what the radio codes in the OOB's were set

to . This has changed in both WinSPMBT and WinSPWW2. Now every company, platoon and section reads the radio codes and if the

OOB's are set up with low radio chance then that's what you'll see in the game. The main HQ unit will always get a radios. This change
affects two things mainly. 1) Calling for artillery will not be as easy as it once was and units from a formation will not be able to wander far
from their "0" unit lead. If they do it becomes harder to rally. This is no different that the way the game has played in the past but in the
past most units had radios. Now there are fewer units that do especially in the WW2 and just post WW2 era. One example would be
snipers. Snipers in the game have acted as scouts, Forward observers and snipers. There are far fewer snipers in this version of the game
that have radio contact with artillery. We expect that this change will take some players who were used to picking almost any command
unit as a Forward observer a bit of time to get used to . The effect is far less in the game on "modern" era armies
3) You will see a further addition to the HQ menu. You will now see ' R ' or ' * ' in the HQ menu list of units. The leaders with the R have a
radio and as always in SP only leaders ( the x0 ) with radios can call arty so if you see a x4 unit with a radio it doesn't mean he can contact
the artillery only leaders can do that. That aspect of the game has not changed but this change makes finding he leaders with the radios
easier. As well these are colour coded and match the messages you would see at the bottom of the battle screen when you click on a unit.
A white ' R ' or ' * ' means " in contact" and all that means is they have C&C link to their immediate superior. A yellow ' R ' or ' * ' means
there is radio contact and a red ' R ' or ' * ' means the unit is out of contact with it's immediate superior. All of this is handy to know at a
glance. If you are playing with
a nation that has few radios you'll probably want to be careful where you put them. This allows you to find them without having to check
every leader in the game

Rally
This is seperate from contact it just allows superiors to assist if you have it.
There is no such thing as rally points units can keep rallying till they fail there rally check.
Unit screen under its name first entry is rally.
Think this decreases by 2 for each attempt in that turn but can keep trying till it fails.
Again from the GG

Back to game detail, still on command and control here. Your commander must be in a fit state to rally subordinates, if he is retreating or worse,

then he has

no command influence, so you may need to rally him first! Also, before you do rally subordinates, check the commander's status, as

if he fails a rally on a subordinate, that is all his rally chances gone for this turn, it can be embarrassing to have rallied all your men back to 'ready'

status, and be about to move forwards to find the platoon (or company!) commander is 'pinned' because you forgot to rally him a little in the

process. Do not just select units and hit the 'R' key is the motto really, look at all the subunits of a formation, and their current state and plan your
rallying. Also note that rallying comes from the top down, hitting the R key on a squad will use the Company Commander's rally attempts then the
Platoon Commander's before trying the squad sergeant's. This may not be what you wanted, again, think a bit before poking that R key. When a
unit fails to rally itself or its subordinate, its rally chance statistic is set to 0 until next turn, this confused some end users who thought the unit was
a hopeless rally case, no, zero just means that it has

failed a rally attempt, and so cannot rally again this turn. The number returns at the

beginning of the next move.

May I suggest you read the game guide I read it years back & have no intrest in going through it again so I get the terminology right.
If you find searching easier in PDF format rather than HTML download it here http://forum.shrapnelgames.com/showthread.php?t=45615&highlight=Format
Try searching for radio or rally or doing the same on the forum then asking for clarification if you dont understand.