How many handsets will you need? If you need more than one handset, it's less expensive to buy the extra handsets as a part of a cordless phone package. Cordless phone systems generally indicate the amount of included handsets in their model number. Many models are expandable with up to six or even 12 handsets, though you may have to buy some handsets separately to achieve this.
What about power outages? To be completely safe in the event of a blackout or AC power failure, consider a corded/cordless phone combo. These phones have a corded base that will still work during a power outage. Also, since you won't be able to charge your handsets, take battery life into account when shopping for a cordless phone.
What features do you need? Cordless phones can vary quite drastically by their feature sets. The most robust models offer link-to-cell via Bluetooth, which lets you sync your handsets up to a cellphone line (but make sure the cordless phone in question supports your make and model of cellphone). Other popular pluses include talking caller ID, call screening and/or an answering machine. Not everyone will care for these bells and whistles, however. At the very least, consider a cordless phone with a 50-number phone book (or larger), speakerphone and voice-mail indicator. Backlit keypads as well as conferencing and intercom features are also appreciated by users.
Do you need two phone lines? Some cordless phones support up to two phone lines. Some models offer distinctive ringtones for each line and support three-way conferencing between both lines and a third party. Some cordless phones with link-to-cell and Bluetooth features let you sync up with up to two cellphones as well as a landline.
Don't forget message quality. Don't assume that just because a cordless phone offers crisp, clear sound during phone calls it will sound great when listening to messages it records. If you expect to rely heavily on a cordless phone's answering-machine feature, be sure to consider message quality in your buying decision.