(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.

Do make sure that you are over-insured if anything, and as Chris suggests, don't do dumb things with the property.....no loose handrails, broken steps, etc.

Is it possible to hide phone number from the listing?

Our storage units were broken into down below in the basement by these neighbors, nothing was done.

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. 

Anything longer than that you'll need to call the city and find out what is required, and sometimes that can take many phone calls until you get the right person.

Is he able to kick him out if rent is paid on time every month and no parts of the lease have been broken?

Might be easier on a brief phone call.