Every letter may not be read by the Representative or Senator personally, but most are at least been read and recorded by a Congressional staff member. When staff members start to see several letters or receive multiple calls on one particular issue, they are put on notice that constituents care about the issue. These staff members then advise the Representative or Senator on which direction he or she should vote. When members of Congress are unsure of how their constituents would like see them vote on a particular issue, they often use the amount of public input received as a barometer to gauge their voters' concerns. While all forms by which you contact your Members are useful, House and Senate offices do acknowledge a priority scale.
Personal visits have the most impact.
Phone calls and hand-written letters are next, followed by post cards, then emails. If time or other constraints only allow you to send an email, by all means you should do it, because it is still important. But if you have additional time, you may want to consider taking the extra step of writing a letter, making a call, or paying a visit. The more time and effort you put into contacting a member of Congress, the more thought they are likely to give to your issue. Members of Congress can be contacted via phone, email, fax, or direct mail.