Skype for Business Server vs. Online

Stefan,

Unfortunately, there is no simple answer. The answer will depend on your specific circumstances. Skype Online may ...

- cost less or cost more than on-premises Skype for Business

-- things to consider: undepreciated assets, Azure Express Route costs, per minute charges associated with some Skype Online services

- provide increased relaiability as compared to an on-prem deployment; especially if you currently don't have a strong operations team OR if you have deployed an under-powered Skype for Business design (too few servers, not enough RAM or CPU, inadequate resiliency)

-- although, some well-staffed on-premises Skype for Business teams I have coached have delivered almost 100% availability

- provide additional functionality for your users

-- this is absolutely the case related to things like Broadcast Meetings; however, Skype Online Call Queues still lack some features compared to on-prem RGS (response group services)

- may provide enhanced security OR may contravene security and data residency rules for your organization

- should eliminate the need to deal with hardware refreshes and patching cycles; although there will likely still be some on-prem hardware (for AD synch or SIP gateways, etc.)

In summary, there is no "silver bullet" or one answer fits all. I have written numerous articles trying to help people make this determination. Here is a single article that steps you through 7 critical steps: http://www.nojitter.com/post/231300501/the-goldilocks-approach-7-steps-to-get-to-just-right (An oldie but goodie. Process is still as relevant today as it was in 2011)

Kevin Kieller, author Success with Skype and Sophisticated Skype