Check out this page: http://recapmycalls.com/faq/compare/
if you still have questions, let me know.
RECAP S2 works on phones that use the AHJ format
It does NOT work on phones with the OMTP jack format.
Not sure what is AHJ and OMTP? Read this: http://recapmycalls.com/faq/headset-standards-ahj-omtp/
Best place to go is: http://recapmycalls.com/faq/
If you cannot find your answer, just contact me via Kickstarter OR open a support ticket at dossant.com/helpticket
Don't see the answer to your question? Ask the project creator directly.