up的up是副词还是介词

是介词，例如：

1、Sometimes I'd even call up at 4 a.m.有时我甚至早上四点都打电话。

2、If he be not apt to beat over matters， and to call up one thing to prove and illustrate another， let him study the lawyer's cases.如果某人不善于详细查看事物，仅限于用一事物去和另一事物对比、解释的话，就让他去见识见识律师怎么办案子。

3、The radio station had an open line on which listeners could call up to discuss various issues.这家电台开放线路，听众可打电话参加各种问题的讨论。

call up的up是副词还是介词

应该是介词，因为up的后面跟了宾语。如：I called up my friend and told him the news.（给…打电话），Your letter called up the days when we worked together fifteen years ago.（使回忆起往事），They were called up right at the beginning of the war.（征召入伍，征召服役）。

句3中使用了被动语态，在被动句中，主语就是主动语态的宾语。所以，综上所述，call up无论表示什么意思，后面都跟宾语，因此，up在这里是用作介词。