Contact information is important but it doesn't have to include a phone or physical address if you are not selling a physical product and you just deal with individuals.
Personally, as long as you have an email address (or even a contact form) I'm happy - I will probably send a very simple request to see how long it takes you to reply and judge on that. If you can only respond to emails during certain times let me know that on the site (either in my local timezone or in GMT - preferably both).
My personal rule is - if it's over $US 500 in a single transaction I do want an address, phone number, company details etc in case you rip me off. Under that it's a matter of 'Caveat emptor' and I'll simply block future charges from you to my credit card.
When you are primarily dealing with companies you will want to make that information available or they will not deal with you. If you occasionally deal with businesses it may be enough for them to contact you via email for full company information (which will probably also include tax information, business registration information, physical address, etc).
From the looks of your site you deal with both - perhaps a split sign up form? One for business which provides phone and physical address information and another for job seekers that doesn't include that information.
However, if you don't supply an address or phone number don't ask me for mine as a client though - I won't give it to you. Email address so you can contact me - sure, name and address for credit card verification (through a valid billing system) no problems. Do not ask me for that information simply to sign up though - I don't expect it from you, don't expect it from me.