iswitchb-default-method

iswitchb-default-method is a variable defined in `iswitchb.el'.
Its value is

always-frame

Documentation:
How to switch to new buffer when using `iswitchb-buffer'.
Possible values:
`samewindow' Show new buffer in same window
`otherwindow' Show new buffer in another window (same frame)
`display' Display buffer in another window without switching to it
`otherframe' Show new buffer in another frame
`maybe-frame' If a buffer is visible in another frame, prompt to ask if you
you want to see the buffer in the same window of the current
frame or in the other frame.
`always-frame' If a buffer is visible in another frame, raise that
frame. Otherwise, visit the buffer in the same window.

You can customize this variable.