This is a real dry year. Haven't had much rain the entire winter. While it is possible in mid-April, it is unlikely. Be aware that rain in California tends to come in heavy storms and might be particularly unpleasant to ride in. Check the weather forecast (a full 10 days is shown on yahoo weather) before you leave.
As for cellphone coverage, there will likely be some spots on the Big Sur coast where phone reception will be non-existent or weak. There may be a few others spots, as well. Say, Highway 1 from Lompoc to 101.