Hello William I just wanted to give my 2 cents since you've been helpful to me in the past. Although my medical billing experience is minimal, my background is mainly as an entrepreneur having built several companies in a different industry. I completely understand your frustration with client acquisition. Sometimes lukewarm clients that lack desperation can be the hardest to convert. I would agree with Linda and Michelle that you should try to create a sense of urgency where there might not be any.
In addition, have you simply tried asking them what is keeping them from making a decision? Sometimes just asking a direct question can you give you deeper insight into why they're dragging their feet which in turn might lead to another question leading you further down the rabbit hole. Don't be afraid to talk to them, remember you're calling to help them...not the other way around
Also sales is largely a numbers game. It's great you have 25 solid leads in your pipeline and while you should continue to aggressively followup, I would continue to make sales calls and mentally move forward in your marketing efforts. This will not only build your existing pipeline but more importantly will keep your spirits up as you won't wonder why those 25 leads aren't calling you back; and we all know positive attitude is key to doing sales.
In any case I hope that was moderately helpful. As someone who is also interested in eventually starting my own billing business I would love to know of your progress. Keep me posted!
Brian