Complex sentence: People therefore must often guess if they need to dial 1 +907 or not (if they do not know the actual location of the business or person they are calling), though local calls from local telephones can use just seven digits.
Split into simpler sentences: People therefore must often guess if they need to dial 1 +907 or not (if they don't know the actual location of the business/person they are calling). Though local calls from local telephones can use just seven digits.