Some wireless carriers fear that Apple's iMessage service, which was announced at the Worldwide Developers Conference in June, could hurt their bottom line.

With iMessage, users of iOS devices will be able to chat with one another just like they would send text messages. What is upsetting carriers is that iMessage will allow users to bypass the SMS text-messaging network and the carriers' texting charges.

iMessage will send text messages over a wireless Internet data connection, rather than routing them over the cellular network using SMS.

The service will not be tied to any carriers, and will work on the iPhone, as well as non-cellular devices, such as the Wi-Fi only version of the iPad tablet.

The service will make a dent in carriers' revenues, as carriers are currently charging clients 20 cents to send a text message to a phone, and another 20 cents from the person who receives the text.

Craig Moffett, an analyst at Sanford C. Bernstein, estimated that wireless industry pockets more than $20 billion in revenue from text messaging.

Speaking on the topic, Moffett said, "They are undermining the core business model for an industry that makes most of its money from services that are high priced and low bandwidth, like texting."

Apple has plans to launch iMessage service on Wednesday.