I was recently excused for jury duty for an unrelated medical issue. The clerk did tell me that if I had been approved, I would be exempted regarding the edevice due to my vision issues. The device would have to be examined, certain programs may be removed and wireless made inoperable. So, go ahead and call and ask what you can use. I'm sure it varies from place to place. You might also ask if you could bring an ipod to listen to an audiobook since Ipods can't access online. On an ebook, they make wireless inoperable by activating the parental controls.
When my sister went for jury duty (different county), they said that you can use edevices until you are actually called into a case. At that point, they would lock up your edevice until you left for the day or the case completed.
Knitters and crocheters have the same issues. Some places let you bring knitting or crocheting while you wait to see if you will be called for a case. Others do not.
edited to add: the types of programs that would potentially be removed would be things such as encyclopedias and other information databases potentially involved in expected cases. Dictionary was fine.