The looming shutdown of 3G networks could leave older adults without a critical communications lifeline. All 3G devices will lose service by the end of the year due to a planned transition to newer technologies. Verizon said it would finish shutting down its 3G network by December 31. T-Mobile aims to shut down its 3G by March 31, and AT&T said it would shut down its network last month. Experts say that the 3G shutoff could mean seniors will suffer.