Hello,
You will dial numbers as locals do (you don’t need to add the plus sign or country code 31). In this case you will add a zero in front of the cell number and this is what you will dial: 0618707???. Same dialing pattern for when you’ll use a Holland cell.
I’ve combined your posts. To dial your husband’s US cell you will have to enter +1 followed by area code and 7 digit cell number (or you can use 00 instead of the plus sign). Note that in this case you’ll both incur international charges.