You shouldn’t worry at all about the alarmist report in the Telegraph claiming that relying on your mobile’s address book to remember all your phone numbers and email addresses is “dumbing us down”. Reading and believing it is a far bigger threat to your smarts.
I’m not worried because I remember what a guy named Plato said about writing: that by writing things down rather than committing them to memory, we’d create forgetful people and everything would go downhill from there:
If men learn [writing], it will implant forgetfulness in their souls; they will cease to exercise memory because they rely on that which is written, calling things to remembrance no longer from within themselves, but by means of external marks. What you have discovered is a recipe not for memory, but for reminder. And it is no true wisdom that you offer your disciples, but only its semblance, for by telling them of many things without teaching them you will make them seem to know much, while for the most part they know nothing, and as men filled, not with wisdom, but with the conceit of wisdom, they will be a burden to their fellows.