Cordless phones used in homes emit electromagnetic radiation, but not ionizing radiation, and hence the unit "milliSivert毫稀", which is for ionizing radiation, should not be applied.
The frequency used in cordless phones is normally lower than that use by mobile phones, it is in the UHF (ultra-high frequency) range. Those illegal phones (i.e. those cordless phones not approved by the Office of Telecommunication Authority) may have frequency the same as that of GSM mobile phones ( at 900 MHz).
Because of the short distance of coverage required by cordless phones, the transmitter is of very low power. For those legal cordless phones on sale in Hong Kong, the eelctromagnetic radiation emitted must comply with the guidelines levels recommendated by the Internaltional Commission on Non-ionizing Radiation Protection. For exposures of electromagnetic radiation below that level, there is no scientific evidence that any adverse health effect, including that to the brain, will be resutled.
most of the indoor phone use frequency band of 900MHz / 1800MHz / 2400MHz or 5400MHz, which is classified as microwave. however this home use devices have limited power of 10mW (1/100 watt) so it is not very harmful to your brain. Compare to a GSM Phone it emit a maximum of 2W!! moreover most of the cordless phone you get from teh market have different kind of safety international recognized approval (FCC / UL / CE / GB...) which proof it SHOULD NOT be harmful to human body so you do not have to worry...