I prefer Sorenson because of better video quality.
I did use Purple and their video quality is terrible.
Right now Sorenson is better (my opinion). Purple released a new app, but it sucks. They need to do better than that.
Just want let you know that nTouch Mobile and Purple app look same, because where the mail and setting that same as App. I would say both are use third party software by who? I do not know but again I am not going to digging more...
Both is not helpful as Z5 is helpful on my iPhone. So I can look myself before I dial the call.