Can we keep our current desk phones?

Depends on what kind of desk phones you have.

Currently Flexfone supports some desk phone models from LG, Snom and all Yealink models.

Yealink is the most common desk phone in our customer base, and the one we recommend for the best Flexfone experience. With that said, a Flexfone reseller will gladly take a look at your current setup, and determine if it's compatible with Flexfone.