Whether To Remove Phone Number From Your Online Form

I have always advocated an online form that is as short as possible - typically 4 fields: name, email, phone, company name. Well I just read a post by Jason Stewart that is making me think that even that is too long. He mentioned that conversions doubled - yes that means a 100% increase - when they stopped asking for phone number on the online form. This is amazing to me. Certainly, phone number provides some value if the prospect does not respond to your email. But if you immediately send a good email response to that prospect and they don't respond, what is the likelihood that that prospect will respond to a phone call, assuming the phone number is even accurate? And is that percentage high enough to offset the twice as many prospects you would have if you removed the phone number?

So I leave this up to every vendor to test, but now I have to decide what will be my default recommendation to our vendors. You can probably guess which way I am leaning.