I had an answering service in the early years. The problems I had are as follows:
1. With any forwarding there can be an odd delay, as in ring...ring...... .....ring...ring. What you can get is a "double-space" between rings.
2. I was continuously training the answering service people how I wanted my call answered. It was a rapid turn-over job.
3. As they got busier my calls would get put on hold. Not quite the service I was looking for.
What I'm considering now for the next few weeks is leaving my cell number on my answering machine (as in...I'm on the job, call my cell or leave a message). Then they have the option of calling the cell, leaving a message, or both.
I looked at new cell phones yesterday and you can plug a better antenna into them. They all have a port at the base of the antenna. You might try that in the truck or office.
Dave