Camping on the JMT

In general, is most the camping free when hiking the JMT or would i need to make reservations with campsites in advance? Also, purely to check in with family back home, are there any wifi spots along the trail at all? I'm assuming there isn't but my Mom back home in England would probably appreciate at least one little email checking in over the 28 days! Thanks in advance for your help. This site is such an amazing resource!