I would always use a specialised recruiter rather than facility recruiters for this type of target. I can recommend Annette Madden at Adkins. They will also help guide you to the most suitable venue for your required target - it depends upon the speciality which you require. Annette is superb, has massive knowledge to help you!
In my experience Adkins Medical have always been helpful - always willing to advise, efficient delivering on projects, nice people to work with - always willing to cooperate on providing information on ongoing projects for my clients and cost effective. They are always my first choice for telephone research.
Our company has used ARG for all it's recruitment over the last 10+ years and they have consistently provided an excellent service. The project managers are helpful, attentive and never give up trying. They tackle difficult problems and 'hard to reach' respondents with experience and intelligence. Attendance rates are extremely high as ARG ensure they implement a stringent confirmation process. Adherence to guidelines is second to none. Throughout our working relationship, we have never considered going elsewhere - why look further when you get excellence every time.