On Internet, general rule of thumb is that when someone sends you an e-mail, you're expected to have read it within 24 hours.
If you sell a hands-on product, like a high ticket item or coaching program, you might want to be notified of a sale instantly, even if you're away from computer, so you can follow-up with your customer within minutes and impress heck out of them.
This can be done with your web host's existing control panel, requires no programming, AND could be applied to any payment processor like Clickbank, StormPay, 2Checkout, etc. as long as that processor sends you an e-mail after every purchase.
For this you need a cell phone. (Did you know your cell phone most likely ALREADY accepts text messages through e-mail? I didn't until I looked into it.) Figure out your SMS e-mail address:
If your provider is AT&T, your SMS address will end in: mobile.att.net If your provider is Cingular, your SMS address will end in: mycingular.com If your provider is Nextel, your SMS address will end in: messaging.nextel.com If your provider is Qwest, your SMS address will end in: qwestp.com If your provider is Sprint, your SMS address will end in: messaging.sprintpcs.com If your provider is T-Mobile, your SMS address will end in: tmomail.net If your provider is Verizon, your SMS address will end in: vtext.com If your provider is VoiceStream, your SMS address will end in: voicestream.net
Don't see your carrier in this list? Call them up and find out if you can receive SMS messages through e-mail.
The first part of your SMS e-mail will be your phone number, without any spaces, dashes or parentheses. So if your cell number was (817) 555-1212, that number without all those extra things would just be 8175551212.
Put two together. So if your number is (817) 555-1212 and your cellular carrier is Verizon, your SMS e-mail is: email@example.com