States have different rules about faculty educational requirements. So do different schools
. As a general rule though ... you can teach undergraduates with an MSN and maybe teach a couple of graduate schools (e.g. supervise clinicals, etc.). However, your career advancement possibilities will be limited with only an MSN.
Some of the higher level roles in academia (and maybe some of the more desirable teaching assignments, depending on your interests) may not be available to you. For example, large research universities often require PhD's for the higher ranks of the professorate (full professor, associate professor, tenure, etc.) -- or to be a program director, course coordinator, etc.
In short, with only an MSN, you will have job opportunities -- but not as many at the higher end of the pay scale and responsibility continuum as you would with a PhD.
You'd have to check with your local schools to see the particular requirements where you live.