I don't remember calling the checkpoint at kilometre 6. We stopped on our way up and on the way back. Just registered our names and where we were going and for how long.
The emergency/payphones don't take coins for obvious reasons. I'm still trying to figure if they take credit cards but I still think they don't. Much safer to just buy a prepaid card.
Now for cellular service: don't rely on your cell phone. There is limited coverage but only in very specific places.
If you have Rogers or a GSM network cell phone, it will work in Amos but nowhere on the James Bay Road.
The limited coverage works on a CDMA cellular network.
If you have a Bell Mobility, Telus, Northern Tel, Telebec, Aliant Mobility and many others that are part of the CDMA then they'll work in the limited areas. (I believe other companies included are Koodo, Virgin, SaskTel, MTS) For American visitors I think Sprint PCS phones (not Nextel ones) will work on CDMA and I think Verizon too.
Click on this link:
http://www.telebec.com/ and you can click on "English" which right now is small and found at the bottom of the page and then on "Mobility." Find "coverage" and click on it and it will show where there is coverage.
Matagami has coverage as well as Chisasibi but Radisson does not. There is some coverage in communities and hydro worksites away from the James Bay Road.