▁been ▁described ▁as ▁North ▁Korea ' s ▁" l if eline ▁to ▁the ▁outside ▁world ." ▁Much ▁of ▁the ▁China - N orth ▁Korea ▁trade ▁goes ▁through ▁the ▁port ▁of ▁D and ong . ▁ ▁Chinese ▁cell ▁phone ▁service ▁has ▁been ▁known ▁to ▁extend ▁as ▁far ▁as ▁ ▁into ▁Korean ▁territory , ▁which ▁has ▁led ▁to ▁the ▁development ▁of ▁a ▁black ▁market ▁for ▁Chinese ▁cell ▁ph ones ▁in ▁the ▁border ▁regions . ▁International ▁calls ▁are ▁strictly ▁forb idden ▁in ▁North ▁Korea , ▁and ▁viol ators ▁put ▁themselves ▁at ▁considerable ▁per il ▁to ▁ac quire ▁such ▁ph ones . ▁ ▁Tour ists ▁in ▁D and ong ▁can ▁take ▁speed bo at ▁r ides ▁along ▁the ▁North ▁Korean ▁side ▁of ▁the ▁Am n ok ▁River ▁and ▁up ▁its ▁trib ut aries . ▁ ▁A ▁common ▁wed ding ▁day ▁event ▁for ▁many ▁Chinese ▁cou ples ▁involve ▁rent ing ▁boats , ▁putting ▁life ▁pres er vers ▁on ▁over ▁their ▁wed ding ▁clothes , ▁and ▁going ▁to ▁the ▁North ▁Korean ▁border ▁to ▁have ▁wed ding ▁photos ▁taken . ▁ ▁Memory ▁cards ▁and ▁ted dy ▁be ars ▁are ▁reported ly ▁among ▁the ▁most ▁popular ▁items ▁for ▁North ▁Kore ans ▁sho pping ▁in ▁D and ong . ▁ ▁Cross ings ▁ ▁Border ▁security ▁ ▁The ▁ 1 , 4 2 0   km ▁border ▁between ▁North ▁Korea ▁and ▁China ▁has ▁been ▁described ▁as ▁" por ous ". ▁Many ▁North ▁Korean ▁def ectors ▁cross ▁into ▁China . ▁ ▁The ▁Chinese ▁government ▁transferred ▁responsibility ▁for ▁man aging ▁the ▁border ▁to ▁the ▁army