I pretty much agree with ytti about this, but in some more detail.
First, none of this makes an iota of difference if the kit is operating on voice, a single DS0 or terabits, you ground for other reasons. If you have such a high EMI that grounding might help with errors the actual problem is with whatever is spewing the crap, and likely as not wiring the device to a giant antenna of a ground wire (never loop) will only make things worse.
If you have a DC powered device you REALLY SHOULD ground separately. There are valid safety reasons for this and the cost of doing to handle the safety level is trivial (wire to the rack, rack to a building ground wire which should already exist). DC systems are almost never "grounded" on one or other of the supply lines, and most DC hardware does not connect the case to ground so this is critical. The screws and friction holding the device to a rack is not acceptable, you need a separate wire.
Next, for AC devices.
Those that are optionally DC, or dual supply may or may not have the case grounded to AC ground, so should be grounded for the same safety reason.
Now that (personnel) safety is out of the picture the answer shifts.
If the device directly takes a copper / coax from outside the room I'd strongly suggest grounding to help prevent any surge / lightning damage continuing down a path (also an argument for demark racks containing isolation & protection devices).
So if none of those apply you certainly don't need to ground and will be unlikely to get a benefit from doing so; although you may reduce occurrences of some oddball problems, I usually see a few cases a year where bad grounding may well have contributed to a problem, usually these are cases that take weeks to diagnose and repair, and even if the hardware is replaced under support the time lost may make it worthwhile to do.
All of the above, plus having a safer "standard practice" is largely why most telco's will have pretty stringent grounding policies (at least at their own facilities).