What are the power levels/channels allowed by each country?
General guidelines for power transmission based on location is tricky because the per-channel nuances vary with the hardware design (depending on how the module manufacturer achieves FCC or ETSI approval).
North America and Japan: Up to +20 dBm ERP (Effective Radiated Power) without restrictions (100 mW). In certain circumstances up to 1 W (may require special permission).
Europe: Up to +13 dBm ERP or 20 mW, channels 11-26, without restriction.
FCC testing, applicable to U.S. design only, has strict rules about band edge restrictions at the upper edge of the 2.4 GHz band. This does not allow for running at max power on Channel 26 (since even at +3dBm you will bleed too much outside of the spectrum to pass FCC). Also, if your design has external PA's driving +10 to +20 dB of gain, then usually the power will need to be reduced for Channel 25 in order to pass this restriction as well. In these cases (channels 25 and 26) the module manufacturer, or whoever did the FCC qualifications on the RF design, will need to be consulted for what is an approved power range.
Our EM35x chipset will take TX output settings (in software) of up to +8 dBm. This does not include any external amplifier gain from either a PA or FEM (Front-End Module). The customer using these will need to be careful as most amplifier solutions introduce +10 or +20 dB of gain after the signal leaves our chip. For more information on PA/FEM usage, please refer to the Knowledge Base Article entitled 'FEM usage for EM35x chips'.