Southwest Airlines said Wednesday that it will begin offering passengers with iOS devices the ability to use iMessage, Apple’s proprietary messaging system, from gate to gate. The new service, which will be available to anyone with a device running iOS 5 or later, will cost $2, and work throughout the flight. Southwest is partnering with Global Eagle Entertainment to offer the connectivity. The airline said it plans to expand the service to Android devices next year. Southwest offers passengers in-flight Wi-Fi for $8, but it clearly feels that some people want to stay connected with friends, co-workers, or family, but don’t want to spend that much. The airline is able to offer the service gate to gate because of a recent decision by the Federal Aviation Administration to allow passengers to use portable electronic devices below 10,000 feet.