This Sunday, just after midnight, Sprint will finally pull the plug on the legacy push-to-talk iDEN network it inherited when it purchased Nextel. The move is designed to free up spectrum and cell towers for the carrier's growing LTE network. That means the last full day of iDEN service, for those still using phones running on the network, is Saturday. After that, iDEN devices won't work — even to make 911 calls.

Sprint pulled all iDEN phones from its stores shelves last year, and has been warning of the impending shutdown since 2010. The carrier has been pushing its CDMA Direct Connect network as the replacement for iDEN, because it features push-to-talk service and has about three times the coverage area of iDEN. At its peak, iDEN was used by about 6 million subscribers in the US. Sprint hasn't said how many are still connecting to the lame-duck network. But if you're one of those out there with an iDEN handset and haven't yet gotten the message, it's time to head into a Sprint store.