I've had good experiences with i711Relay using AOL Instant messager.
The problem with the TTY is that it's cumbersome to carry around. With my cellphone I can do relay calls because I can do AOL IM chats on that.
As I said I really like it for at home on a landline.
With my cell phone I use Hamilton CapTel most of the time and like it. The difference between us maybe because I prefer to use my voice, which is necessary with CapTel.
I am in a semi-rural area and the portable TTY will be a backup if I have need in an area that does not have a good enough signal for the simultaneous voice and data that Hamilton CapTel needs. It will be left in the car and not carried around all the time.