josh_marchant,
Those phones don't look any more durable than the 112 is, but to each their own. if you need a rugged cordless phone look at the Engenius Durafon or Durawalkies; which are analog not SIP.
Regardless though a SIP Device will work with the MiVO-250 if you have the licensing for them. If you are removing the 112 and replacing it with a Yealink then you will have the licensing you need. Keep in mind though that features support is by the lowest common denominator. This means it has to be supported on both the phone and the MiVO-250 unless it is a feature that is P2P or Multicast between devices.
Thanks,
TE