Can't remember when or where (though it could have been Reuters) but there was a report of a company looking at making a combined Smartphone\DECT phone. When away from your DECT base station it would function as a normal mobile. However, once in range, it would use either Bluetooth or Wi-Fi to connect to your base station and allow you to make calls over your landline. The article speculated that Wi-Fi would be the prefered option as it has a similar range to current DECT phones.
I've been expecting something like that for ages. It's a pain in the perverbial having to enter all your numbers in your mobile AND DECT phones.
I know this doesn't exactly asnswer your question, but it's (I think) interesting and relevant!
You look like you want to go away, But I know you’re gonna stay. For although your heart is in L.A, Your head is in my fridge. There’s flowers in your hair, they're not real their made of silk. There’s a note in your mouth, to remind me to get milk.