When acquiring a new phone system or upgrading an old one, good integration with mobile is an important factor to most organizations. IMO, FreePBX is weak in this regard; I’d rate it a C. The 3CX app is a step up, perhaps C+ or B-. A few expensive hosted systems such as RingCentral and Dialpad would get a B. I’m not aware of anything that comes close to an A.
If a third party offers good mobile integration for FreePBX, IMO Sangoma should welcome them, because it will result in more deployments. You may lose the Zulu sale, but you’ll sell more other commercial modules, support, trunking service, appliances and phones.
That said, I took a look at the Ringotel site and came away disappointed. There is no description of features, pricing information, robustness, etc. I hope that @arroinie will be permitted to post those details here.
I admit to never having even tried Zulu, because numerous credible posts in this forum indicate that it is not yet as stable as the Groundwire app I’m using now. But that’s far from perfect; when staying in an area with poor network coverage, I manually change Follow Me to make a mobile voice call instead. I had recently been working deep in the backyard and experienced several calls with really bad voice quality; the Wi-Fi signal from the house was too weak. (Yet weaker would have switched to mobile data and been fine.) The solution was installing an old unused Ubiquiti outdoor AP onto the roof of the barn.
We shouldn’t have to resort to such measures. Why can’t we have grade A mobile integration that just works?