"fb friend" wants to be phone buddies.please help.?

[Nic]

I have a FB "friend", we went to the same grade school although i dont remember her then...we have have been communicating via FB emails and a few phone calls. We get along great!we have alot in common, have many similiar interests and values, and i genuinely enjoy our "facebook friendship".
the problem is, she wants to chat on the phone on a regular basis. she ends an email or message with "call me tomorrow"--and i often have not done so 1.) because the email wasnt read immediately and 2)i just had other stuff to do. We had a few great conversations on the phone before, but now she makes me feel bad about not calling her back, EVEN THOUGH WE ARE frequently, if not daily, in contact via FB. shes a great person, i enjoy getting to know her, but, I only know her thru FB.we dont hang out.ive tried telling her honestly and bluntly, that chatting on the phone just isnt in my schedule, but she sees me on facebook all the time and figures i do have time to chat. i dont want to her her feelings, but i dont want to feel like a bad person for not calling her on the phone. please help.