Complex sentence: Within a decade, however, 760 was strained to the point that a new 442 Area Code was scheduled to be split from 760 such that the portion of 760 serving San Diego and Imperial Counties would now instead be served solely by the new 442 Area Code.
Split into simpler sentences: Within a decade, however, 760 was strained to the point that a new area code would be necessary to serve the area. It was decided that the 760 Area Code would split such that the portions of San Diego and Imperial Counties currently served by 760 would change to a new 442 Area Code.