Newer android and ios phones are using BT 4.0 chipsets which may cause problems with older BT gateways.
I have seen Sparkfun bluetooth rotary phone working with some phones but not others.
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www.sparkfun.com/products/9803Two years ago, I tried to build one like that but using an old Nortel touch-tone phone. Sadly it did not connect to my Samsung m300 flip phone and I gave up.