Businesses of all size face a fundamental question when planning for a UC deployment...
Is it best to (1)continue to use multiple vendors or (2) select a single vendor to deliver all UC functionality?
Organizations that choose option #1 do so to minimize loss of functionality by selecting the best technology/platform for each business requirement.
Organizations that choose option #2 do so to streamline the user experience and reduce the number of platforms / passwords that users have to manage.
There are benefits and challenges with each approach.
When building your UC strategy, here are 5 questions to ask stakeholders that will help answer the big question up top!

o Voice and Telephony
o Conferencing
o Messaging
o Presence and IM
o Clients
o Communication Applications
o Document Sharing
3) Which of the following will drive the decision most: Cost, Functionality, or Reliability?
4) What existing / future business applications do we want to integrate with our UC solution? (CRM, Call Center?)
5) On a scale of 1-10, how important is it to have a single user interface, login/password drives our UC solution?
Once you collect the answers to the above questions, you'll be ready to start evaluating providers to find your ideal UC solution.