I like the Duo product as the 2FA solution with Pulse secure. This has a very flexible setup to use app, text or voice phone connections as the second factor and supports even multiple options on demand per user.
Pulse Secure setup with Duo
https://duo.com/docs/pulseconnect
Hi there! Using Radius, you can generate an OTP and send it via SMS or email. Here is a link to this send quick Conexa solution: http://www.smsala.com