There seems to be some weird hiccup in the Chrome to Phone extension that causes messages to get stuck if you're already online. A lot of people seem to be having this problem. I discovered that if you are on Wifi switching to 3G sends frees the queue up and fetches your links. I suspect going to airplane mode and back would do the same thing if it gets stuck when you're on 3G, but I haven't seen it get stuck on 3G yet. Maybe Chrome to Phone is having problems finding people's phones when they're on the Wifi, or maybe router issues are involved. Anyway, try it, it works.