Time Zones for Leads & Contacts
If you call on clients nationally, you may have figured out that it often makes sense to make your sales calls starting in the Eastern time zones and working towards the West. For example, if you live in the Central time zone and start your business day at 8am CT, you may not want to call on clients in the Pacific time zone first thing in the morning (6am). Furthermore, you may want to start your calling on the Eastern time zone because they will be at lunch before you know it. Consequently, it is very helpful to be able to sort your Leads or Contact calls by time zone. There are a number of ways of achieving this, including some plug-ins for the Firefox browser, but I prefer a solution native to salesforce.com that doesn't require me to be on a specific computer and using a specific browser. Consequently, I created this Time Zone custom formula field to identify time zones.
The formula is based on the area code for the standard Phone field (same on both Leads and Contacts so you should be able to create this field on either object using the same formula). You could also substitute the mobile phone, but many people don't change these when they move. I for example, moved from Texas (Central) to Colorado (Mountain) but still use my Dallas-based cell phone number. Consequently, even if you call the mobile number, basing the selecting of who to call from time zone off the office phone isn't a bad idea.
I should note that less than 5% of the area codes are split among 2 time zones, so I have coded the time zone to the LATER of the two. You could also create a similar formula based on State/Province vs. area code, but be aware, there are more states that split time zones than area codes that split time zones. Finally, I only addressed Pacific, Mountain, Central and Eastern time zones. Others are grouped under "Other", but you could expand the formula as you like. Special thanks to my daughter Hannah for reading the area codes out loud while I typed them into the formula :)