I've played quite a bit of email and phone tag with different departments representing the City of Jacksonville and haven't been able to get a solid straight answer.

Would also love to speak over phone/zoom if anyone is willing. 

(What kind of cold calling software can I get to acquire phone numbers?)

(There are other ways to obtain/develop that evidence - such as using certified mail or my “practical advice” below.)In your case, because your friend found the letter inside the mailbox of the last known address, you now have specific evidence of having mailed the letter “…by first class mail, to the tenant's last known place of residence” - “Unless other arrangements (had been) made in writing by the tenant…”Again, in my (non-lawyer) opinion, you’ve complied with the letter of the law as to your concern - “Unless other arrangements (had been) made in writing by the tenant…”[Practical advice: Where I self-manage, in my “Notices” section of the lease, besides my physical address, phone numbers, etc for notices to me, I provide two email addresses for myself, and state in that part that email is my preferred method of communication.

You can succeed even now if you have enough money so you are in control of when to sell, and your tenants are screened more than well.  

Is it possible to hide phone number from the listing?

I called up Harris County, gave the address and they let me know over the phone.  

if you could find a way to do it virtually or by phone calls, you could definitely get some business because i’m interested. 

The company helps with the rest of the stuff like rent collection, late payment follow up, advertising vacant units, showings, tenant screening, leasing, renewals, reports, and evictions (which is a corner case).

Might be easier on a brief phone call.