I need help ladies found woman's number in husbands wallet

Ok I trust my husband but being cheated on in my previous marriage made me more aware of the signs, so I found a torn piece of paper in his wallet while I was putting in a love note so he can read it the next day and it just says nabina with the phone number and a fucking little heart to dot the i. First of all we have cell phones so why put it on a paper. I questioned him and he denies even seeing it before but i got it out of his wallet. What should I do call or text.the number, ignore it does anyone have any ideas please help.