He kept in touch with people with a mobile phone用with还是on
问题描述：
He kept in touch with people with a mobile phone用with还是on
是with a mobile phone还是on a mobile phone
答
with 或 by using
He used a mobile phone to keep in touch with people.怎么解释呢？ON 为什么不行呢on a mobile phone 有正在打电话的意思