基本案情沈某系中国联通有限公司某分公司(以下简称联通公司)的手机用户。2003年9月4日,沈某与鱼商唐某签订金枪鱼购销协议,约定由唐某于同年9月6日中午前向沈某提供金枪鱼23担,交货地点由唐某提供,联系方式为手机通知,在协议书中具立双方的手机号码,并约定若一方违约应赔偿对方违约金人民币7000元。同年9月6日上午至7日下午,沈某在事 The basic case Shen a Department of China Unicom Co., Ltd. a branch (hereinafter referred to Unicom) mobile phone users. September 4, 2003, Shenmou and fish Tangmou signed a tuna purchase and sale agreement, agreed by Tangmou at noon on September 6 the same year to Shen a 23 tuna provided by the delivery place Tangmou contact information Mobile phone notification, both parties in the agreement with the phone number, and agreed that if one party breach of contract should compensate the other party a default fine of 7,000 yuan. In the afternoon of September 6 the same year on the afternoon of the 7th, Shen a thing