But I don't use a landline.....

I just signed Offspring up for Delta's frequent flyer program and it asked for a mobile phone number, and then for a home phone number.  My mobile number is our home number, so I left it blank.  *error* It required me to fill in a home number.  So I filled in my mobile number in that field too. *error*.  WTF?  Now what am I gonna put in?  I don't use a landline.  Ultimately, I put his dad's number in there, but if I need to sign up for Delta's miles myself (which I should do, I travel for business alot lately), I'm not quite sure what to put there.  I guess I'll put Wheeler's cell number there.  But it's just annoying that they are so behind the times that they don't account for people who only use a mobile for everything.  I've used a mobile for everything for 5+ years.  Get with the program people!