50 percent of email is spam and Gmail has had to create multiple invoices to segment the emails that are probably not going to be read.

Snail mail is probably $1 to send something that will likely be thrown out.

Phone calls - we're rounding the corner after the days of auto insurance calls. But the behavior of only answering known callers might be here to stay.

Sms is the best channel at enforcing opt-in and if it's not worth $0.01 to reach me with the message, sms probably isn't the right channel

The city texts are fine, but you can see during campaign season that $0.01 is WAY WAY below their per-voter spend for their ad campaigns. I get texts from everybody in the race, even "thank you, I'm doing great, please re-elect me" texts from incumbents.