Mobile messaging service WhatsApp plans to move its iOS program (which delivers free SMS-like messages to other WhatsApp users) to an annual subscription model rather than the one-time fee the app currently charges. The subscription would be very low-cost as well -- the first year free, then just $1 per year afterwards -- but would increase revenue and move the app to the same model the company uses on all other platforms it serves. The plan may not affect current users, but will face competition.
