= 0Mt, CellMapper not require mobile data, but then not all feature supported. CellMapper require mobile network connection but not need mobile data. So you can use Cellmapper also without SIM (Some phone only supported and require API 4.2+) or roaming free.
If you have small data plan, we recommended disable Instant Upload and Estimated Freq bands and Bandwidth support. We recommended enable WIFi Auto Upload so app will upload data points automatic when you have connected to WIFI.
Map page require internet connection but you can use that on WIFI.
Feature what not working without mobile data:
* DC-HSPA+ reading
* LTE-A reading