I personally would not phone someone that just gives a mobile.
If you have both numbers on, and i was requiring the services i would phone the land line number first and then the mobile.
Dont forget on are supposed to have your company address on all your flyers as stated by trading standards.
But since many do not, i wouldn't go near a company that give no address and just uses a mobile, very un professional, and a sign to steer clear, because you cannot trace them.
If you want to be treated seriously like a serious professional you should give your adress, land number and phone number on all your flyers/business card etc.