The reason why you want italics rather than quotes is this:
Telepathy is private. And you can play with that. Someone else can be talking and in the room, while your telepaths work out a plan.
If the telepathy is interspersed with dialogue that everyone in the room can hear, it's a very good idea to have a visual cue that reinforces and tells you that.
It should be differentiated at a glance from speech to reduce confusion. The italicized telepathy would be great, because there's already a convention towards italicizing thought.
That doesn't necessarily mean that you have to italicize thoughts outside telepathic communication. The sentence: The poor man's gonna die of fright, he thought. does not have to have any italics at all, and you'd know what's going on. In fact, it could be very annoying to have every bit of inner dialogue italicized, if it happens frequently. And not having inner dialogue italicized will, at a glance be different from telepathy. Otherwise you might have to add "to himself." This will really depend on frequency, how it looks, and what it's like in context.
Like Mark says, you can do whatever you'd like.
As long as you are internally consistent, and it doesn't look wrong, you can do what you like.