Actually it works fine...
the iPhone works great, for me. Either using the speakerphone, t-coil mode, or with an ALD.
I wear t-coil capable hearing aids (with bluetooth also)
I have an iPhone 3G and use the bluetooth connection via my Soundgate neckloop (t-coil) to hear and talk with my iPhone. I also listen to music and audiobooks.
There are generic assisted listening devices (ALD) available to do the same thing my Bernafon Soundgate does with my aids (Bernafon VR9 CP). I am extremely happy with the device, allowing me to have clear cellphone calls and listen to music and books. The Soundgate can also link to the TV.
The main drawback is the (rechargeable) battery life of the Soundgate AND the iPhone.
I suspect that similar ALDs are battery restricted as well.