My friends that sell stuff on ebay are raving about a cool ebay tool called ahTXT. When a buyer has a question and send the message over ebay to the seller, the seller is notified via text message by ahTXT. Think about it for a minute and you will see the benefit of using such a service (which is free by the way). Let's say you are selling something and a potential buyer has a question. You will be notified immediately via text message, so you can log into your ebay account and answer that question at your earliest convenience.
I talked to the developer of this cool tool (Neil), and he is working on added features that will make this application even more helpful.
I've tested this cool application out, and it works great.