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This is just a paragraph from the phone I was thinking of and it has said you must subscribe for caller display to work or are they just referring to the unwanted call business.
////Simple to use and with a large display, this BT Decor 2200 corded phone is easily accessible, stylish and highly functional. Bursting with features it contains a nifty 50 number memory, enabling you to easily keep in touch with your contacts - while the caller ID allows you to ignore all those unwanted calls. (You must subscribe to a caller display service for this to work. Charges may apply. )./////