I’ve often found first-click attribution for telephone numbers on your website can skew sales towards PPC and SEO, changing to last click could redistribute the sales amongst the channels that converted to a call (particularly Affiliates / SEO / Social platforms).

By not changing the telephone number to this principle it can result in attributing the offline sales to old/outdated marketing efforts. (Advertising that has been pulled / plans that are no longer available / creative that has been edited / landing page changes / marketing channels that have been stopped etc).

I’ve found first-click is more often focused towards brand awareness/exposure rather than driving a conversion (sale/subscription)….which creative/marketing effort actually pushed the user over the tipping point to call and commit.