This sturdy metal helmet appears to be a normal piece of headgear, although it will radiate magic if this is detected for. 

The wearer of a helm of telepathy is able to determine the thoughts of creatures within a 6" range, provided the wearer knows the language used by such creatures (the racial tongue will be used in thoughts in preference to the Common, the Common in preference to alignment languages), and there is not more than 3-ft of solid stone, ¼-ft of iron, or any solid sheeting of lead or gold between the wearer and the creatures. 

The thought pick-up is directional. Conscious effort must be made to pick up thoughts. 

The wearer may communicate by language with any creature within range if there is a mutually known speech, or emotions may be transmitted (empathy) so that a creature will receive the emotional message of the wearer. 

If the wearer of the helm desires to implant a suggestion (see the third level magic-user spell of that name under CHARACTER SPELLS in the PLAYERS HANDBOOK), he or she may attempt to do so as follows: 

For every 2 points of Intelligence greater than the subject, the wearer is 5% more likely to be successful; but for every 1 point of Intelligence lower than the subject, the probability decreases by 5%. Thus the subject creature receiving the suggestion gains a saving throw versus magic with a -1 for every 2 points of Intelligence lower than the telepathist, but +1 for every 1 point of Intelligence higher than the wearer of the helm, and if Intelligence is equal no adjustment is made when the saving throw is rolled. 

The helm of telepathy gives a +4 with respect to psionic related attacks[...]. It increases total psionic strength by 40 points.