Both have all the same features and benefits, they are just set up differently. 2-Line CapTel requires two different analog telephone lines to be connected to the CapTel 840. (Applicable charges for an additional telephone line from your telephone service provider). CapTel 840i only needs one phone line and an Internet connection. There may be cost savings on your phone bill if you have “bundled” Internet and telephone services combined (varies by provider).