Are cell phones considered residential lines under TCPA?

(3) Initiate any telephone call to any residential line using an artificial or prerecorded voice to deliver a message without the prior express written consent of the called party, unless the call

No, they are not.

What are the TCPA’s restrictions on collection calls under FCC rules?
The FCC has determined that debt collection calls are not telemarketing calls. Therefore, under the rule the FCC has stated that with respect to autodialed or prerecorded debt collection calls, to the extent that they do not contain telemarketing messages, would not require any consent when made to residential wireline consumers, but require either prior written or oral consent if made to a consumer’s wireless number referring to 47 C.F.R. § 64.1200(a)(1).

Determining whether a cell phone is a residential line seems to be an academic exercise as I believe that any protection related to a residential line is going to be the same of more extensive for a cell phone.

That might be logical depending on your point of view but it is not accurate. The TCPA regulations provide protections for mobile phones that do not apply to residential landlines.

If our esign provider allows for us to send a document by text would this be an automatic telephone dialing system or an artificial or prerecorded voice requiring express consent since we are not sending the text directly but our provider is generating it when we send a document to be signed?

I assume this would require express consent?

text = atds for TCPA purposes. So it would require prior express consent, but the bar for that is low (unlike prior express written consent, which is required for marketing purposes). .