Re: My personal opinion...
If you have a choice that is...
We are currently upgrading and we are going VOIP internally, through ISDN trunking to the outside world. But the new PBX is flexible and will switch over to VOIP trunking.
The problem we have here, in Germany, is that the Telekom is phasing out ISDN. They have already migrated most private households to VOIP, but their VOIP trunking for businesses is not yet ready for the big time. However it will need to be in place soon, as the ISDN equipment providers are cancelling their support contracts as of 2018. That means that they have to get all customers switched over to VOIP before their ISDN network is left hanging in the wind.
They are planning with a 2016 release of VOIP trunking and migrating all businesses by the 2018 deadline.
All of the PBX systems that they currently sell are VOIP trunking capable. But the older systems (like our old HiPath) aren't VOIP capable.
We also looked at a cloud solution, but that was incredibly expensive, compared to upgrading to the new software PBX. The investment for the cloud solution (set-up fee, phones, headsets. switches etc.) worked out to almost the same price as the PBX, yet the monthly running costs were more than twice as high as the local PBX - and would get steadily more expensive as we add new employees.
That is the good thing about the local PBX, you pay a moderate 1 off licence fee for each new employee, which is about 20% higher than the set-up fee for the cloud solution, but the monthly running costs remain the same. For each additional employee on the cloud, you also have an additional 5€ - 18€ a month (depending on capabilities required).
The cloud solution initially looked reasonable 4€ a month per employee, but that was for a pure phone system. Add in softphone (1€ a month per employee), CTI with Outlook integration (2€ a month per employee), Fax (1€ a month per employee), mobile integration (using smartphone to call over landline number - 1€ a month per employee or 50€ per employee one-time fee). Then there were the flatrates for telephony - 9€ per employee per month for European landline flat rate.
The advantage, of course, with the cloud solution is that (depending on bandwidth availability) all employees can make external calls at the same time - but we've never had the situation where all 12 of our channels have been used.