AT&T is set to discontinue all but its most expensive, unlimited text messaging plans, leaving customers with a choice between expensive pay-as-you-go plans or paying for a full unlimited plan. The carrier has confirmed to Engadget that starting August 21, all new customers will have to choose between the $30/mo. Messaging Unlimited for Families or $20/mo. individual Messaging Unlimited, or go with the $0.20 per SMS, $0.30 per MMS pay…
