I work on a few apps that deal with phone numbers. I usually store these as bigint(11) in MySQL. My migrations always seemed to ignore this.

t.integer :phone_number, :limit => 11

Tonight, I found the following method in ActiveRecord that explains this weirdness:

# Maps logical Rails types to MySQL-specific data types.
def type_to_sql(type, limit = nil, precision = nil, scale = nil)
  return super unless type.to_s == 'integer'

  case limit
  when 1; 'tinyint'
  when 2; 'smallint'
  when 3; 'mediumint'
  when nil, 4, 11; 'int(11)'  # compatibility with MySQL default
  when 5..8; 'bigint'
  else raise(ActiveRecordError, "No integer type has byte size #{limit}")

To fix this, try t.integer :phone_number, :limit => 5 instead.

It seems that (at least with the MySQL adapter), limit actually specifies the number of bytes that are using in the column, rather than the display limit.

Hope that helps someone else.