Normally there is a place where you can click to send a response with your telephone number, and the landlord will call you back, or send you an email.
As the other pointed out these are ads that are posted by the landlord. it is the responsibility of the landlord to provide the contact information. We do not have any more information than you do with respect to these advertisements. .
Landlord/Property Manager will contact you directly if they're real. I think you already got below messages that ads could be scams, as we have seen in the past.
Try different rental ads with contact number.
Watch out for scams - if it looks too good to be true, it is.
Several people use Trulia. Trulia does not have the capability to provide more than the person advertising. If the person advertising is the "Landlord" it will be up to the individual person on that ad. Most likely, if the phone number isn't posted, it may be a spam or scam.
Be careful. If you want to check the rates for comparable go to http://www.RentOMeter.com
All the best to you.
Beware: Some properties are not real. Typically if the price looks to good to be true it is. Someone is fishing for you information. Trulia does a very good job of weeding these out but some to make it through their system. I suspect that if you contacted someone and they did not respond it may be one of these.
3190 S. Bascom Ave. Ste 110
San Jose, CA 95124
Office: (408) 688-0510
FAX: (408) 369-0578
Mobile: (408) 828-8607
DRE #: 01830688