Does it state whether it has to be willing two-way communication? I presume that it allows the creature with telepathy to communicate to another creature and hear its responses, but not to eavesdrop on its thoughts?
I personally think that Telepathy is powerful enough without it being ESP or having additional benefits. And yes, it has to be willing conversation.
I read it as:
telepathy: A creature that has telepathy can communicate telepathically with any other creature that has a language. The other creature must be within line of effect and within a specified range. Telepathy allows for two-way communication.
I emphasize the first part here. The creature that has telepathy can communicate telepathically. Nobody else can.
The "allows for two-way communication" clause is for once telepathy is initiated. Other creatures who do not have telepathy cannot start a conversation with a telepath, the telepath has to initiate it.
It's like cell phones where the telepath has everyone's number, but nobody else does. Once he calls you, you can chat on the phone until either side hangs up. You cannot call anyone else, even the Telepath. You don't have his number. You don't have the power.
Otherwise, it has too great of utility in combat for PCs who do not possess the power if they were allowed to initiate Telepathy with the PC who does have the power.