In a case I’m involved in at the U.S. Fifth Circuit, we recently received, along with the notice of oral argument, this notice of the court’s new policy on admitting electronic devices, such as smart phones and tablet computers. Bottom line: you can take your smart phone or tablet with you; you just need to power it down before entering the courtroom. Counsel presenting oral argument or assisting at counsel table may use a laptop or tablet computer, but must not use these devices to take pictures or photos, or to post to social media inside the courtroom.
p.s. (3 Mar. 2015): For some reason, the link to the Fifth Circuit document did not work for me in MS Internet Explorer. I had no trouble using the link in Google Chrome. I haven’t tried it in Firefox.
p.p.s.: At iPhone JD, Jeff Richardson has a detailed post on this topic and on the general use of electronic devices in court.