If you're collaborating with colleagues or clients in different time zones, try to keep in mind a time that will work for everyone. It's easy to forget that while you're in the office at 9 a.m. on the East Coast, your West Coast customers, clients and employees are probably still asleep. Same goes for international workers and clients as well, so make sure you confirm everyone's time zone before you pick a meeting time.
Doug Brackbill, CEO of Line2, a VoIP service, says, "Typical telephone etiquette suggests that you should never call a client before 9 a.m. or after 9 p.m." He also points out that you should keep in mind any holidays that you personally might not celebrate but that others might recognize. You can keep a calendar of international and religious holidays so that you aren't accidentally scheduling a call when they're observing a religious or national holiday.