You can give them your phone number.
The only annoying thing I find about giving customers my info is that sometimes they put me on their spam email list. -_-
I never give my landline or cellphone number to any new client. I do give my Skype handle. You can delete a contact if necessary.
I learned that lesson a long time ago. Clients are no respecters of time differences!
I rarely give out my phone number.
I usually offer to call the client.
Or I use Skype.
Before calling a client, be sure to consider whether your phone number may show up on their Caller ID or cell phone or whatnot.
My rule of thumb: Any client who gets my phone number or who I call on the phone has already set up an hourly contract with me and knows that they'll be billed for phone time with me.
Yeah, I do think about that sometimes. I had 1 customer that was needy but I just never answered my phone and would subsequently email him when I was done with what I was doing. Even then I wouldn't say it was bad, but I do see your point.
I would agree that you may not want to give out your phone number and many users will use skype, or google hangouts for calls. If you would like to have a conference call, generally you would ask the client for the call in number and they may also provide you with a code that you enter to join the conference call.