With most of the northeastern United States hurtling toward super-fast communications, towns in a swath of rural South Jersey fear being left far behind - even off the grid at times. Wireless reception can be weak there, officials say, because of a dearth of cell towers and because Verizon Communications Inc.'s decades-old copper lines, hanging from telephone poles or snaking through underground conduit, hum, crackle or go dead during rainstorms or fog.