Besaid: hotspot makes visiting besaid mandatory, commsphere placed automatically by the hut near wakka and lulus placeKilika: 2 commspheres, both placed automatically, mandatory. One is in kilika village, the other in the temple
Luca: commsphere placed automatically, must visit in chapter 3
Mihen highroad: 2 placed, must visit in chapter 3. One outside the travel agency, 2nd placed in newroad north only if your party successfully destroy the machina near the ledge, not the al bhed. return back to newroad after mission is over for shinra to place commsphere there. Rin will setup all others
Mushroom: Placed automatically if you visit, talk to shinra there.
Djose: Mandatory cuz of hotspot, placed automatically
Moonflow: visit in chapter 3, placed automatically near toblis spot
Guadosalam: visit in chapter 3, placed automatically
thunder plains: visit in chapter 3, placed automatically
Macalania: 2, one placed at entrance, the 2nd placed in lake macalania
Bikanel: visit in chapter 3, placed automatically
bevelle: visit in chapter 3, placed automatically.
Calm lands: 2, one after walking shortly outside of the agency/inspect shinra, 2nd inside chocobo ranch at the far north section
Mt. gagazet: 2, visit in chapter 3 both should be placed automatically, one at mountains base near kimahri, second in the hot springs
Zanarkand: visit in chapter 3, placed automatically
You should have 20 commspheres placed by the end of chapter 3