Do you wear a hearing aid? If so you can get telecoil in the aid.
I would recommend going to a place like Hearing Solutions, they might have some pretty good gadgets
I have 70% hearing loss (Sensorineural) and I use aid when I'm out for maxium hearing. But I have a OK portable phone by AT&T and I find it quite loud sometimes, volume control is good. The only thing is the ringer is too loud. But I never miss a call.
But yeah, check out Hearing Solutions. Shouldn't be hard to find one they're all over the city.