I agree with Treehumper on the speed and percentage of return calls really being the difference in getting the business. I've seen more arborists who lose business because they didn't get back to a new client who called, and that was even in the case of a company who had a F/T office manager who kept saying she'd have an arborist call my friend back. He never did. The solo guy with an answering machine did.
Answering services, from what I have learned about them, adhere to strictly taking name and phone number and dating the message. I would want to know if you can get someone who could do some essential frontline triage (or 'treeage', har! har!) A virtual secretary or virtual assistant that specializes in answering business calls (I don't do that, don't even ask) may be more advisable because they can work more flexibly on doing call backs for messages left, work from a script to get more information so you know more when you go to call back, etc... It may be a bit more expensive on the one hand (hourly rate) but you wouldn't have the employment taxes and benefits to be paying out and actually have a bit more help in the office when things go crazy busy, cut back when things are slow without dealing with unemployment taxes and all that stuff. You'll also know you have the same person taking care of it all instead of who's live at the call center.
Maybe set up a special line to cell phone in the event of an emergency such as "Help! Help! The tree has fallen through my roof!", just like doctors' office now say if you need immediate medical assistance, call 911.
One thing about using websites and the internet for customer interaction is contact forms can collect a lot of that information for you for non-emergency cases. You can have them pick out a service from a list of services you do, have them specify if they need it done by a certain time, and even if they have a price point (like the bridal consultants at Kleinfelds' wedding dress salon do in "Say Yes to the Dress") they need to stay within. No need to limit yourself to getting name, email and phone number and a comment that could be vague or meanders like a stream of consciousness.