Basically your local phone service provider can not see what your CCM is doing with the call on the second transfer. To them it looks like a new call, thus you are getting charged for the second transfer, if there are any costs involved (i.e long distance).
Besides having a CCM, I also have a Nortel SL-100, on that PBX when you assign call transfer to a phone, you have the option of defining the call transfer capabilites as "call transfer all or call transfer intra-group, in other words restricted to the PBX". This is how we restrict most phones from transferring back off the PBX and incurring costs. Most users don't realize that if they receive a call from the PSTN, then in turn transfer the call back to the PSTN that they will incur the cost of the second if there is any associated costs. I don't believe CCM has the capabilities to restrict call transfer so what you have is a user training problem to make them aware of the danger of call transfers to long distance numbers.
