During my rides, I keep a Bluetooth with a single earpiece hanging on my collar. If I get a text message while riding, I'll pop it in and have Siri read the text to me. If my reply is simple, I can use Siri to convert my speech to a text message, (usually, it's just something like, "Right on. I'll reply when I get to the office"). If the conversation can't wait or requires more attention, I'll stop and either continue the exchange or call the person.