Natively, No, the MX700 cannot join MSTeams, and as it is an end-of-sale device, as well as being past it's end-of-sw maintenance date, will not have any further feature enhancements.
However, in saying this, if you have the appropriate infrastructure in place, or have the device Webex Cloud registered (and have the appropriate licencing), then, yes, the device could be used to dial in to a MSTeams meeting, or even have OBTP Join. But without knowing what your environment is in more detail, it's hard to suggest a path for you to take. It would be best for you to speak to one of your local Cisco Account Team or Cisco Partners who should be able to assist in recommending something that will fit with what you have.
Wayne
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