Georg10 - There is one trunk limit. And you mention a gateway - so you ARE in that limit. You are perfectly in the bounds to evaluate all possible scenarios before purchasing.
The pbx edition is designed to give you a very good taste of what 3CX is. It gives you everything you need for a small home/office. 8 sim calls, 1 trunk for external calls, Ivr, Voicemail, Clients, Webconferencing. Other code bases are practically dead.
And you have 8 sim calls. More than enough to test the most common 4-8 port gateway. It's a very good option.
I think your problem is not 3CX itself here. Nor the licensing.
I think you are worried about the gateway and how it will work.
If you are not experienced in VoIP, YES, I sympathize. An unsupported PSTN gateway can give you nightmares.
I will take the liberty to give you some tips. There are 3 fundamental components on a pstn gateway that can really give you a bad taste of the whole voice experience - whatever pbx you use.
1) tone sets. You MUST configure your local telco's tonesets. (Disconnect, reorder dialling tones etc). You get the frequencies and cadences from the telco. Or login to the device and chose the country you are in. If you are not in the usa or europe, cross your fingers. Go here for tonesets and fine your country
http://downloads.3cx.com/downloads/misc/GXPblog/CountryToneSetValues.pdf
2) Hunting. What happens when 1 port is hogged? Where does the outbound call? In which direction? Just make one sim call and leave it connected and make an outbound call. It should ascend, descend, etc
3) Exhaustion. What happens when all ports are in use. If you have a gateway that has more than 8 ports then you disable ports. If you disable 6 ports, you can make 3 calls to prove this test.
Apart from this, the gateway should work. If it follows the sip standard, any device will work. Im telling you from experience. I have seen archaic, prehistoric gateways work back in the days. Now everyone is on sip trunks by the way.. So not sure why you want to end up scratching your head as if you are digging for oil when you can just go to sip trunks, see where you are located, choose a trunk from there and go to their site..
Btw - You can find a legacy template for 3CX on the internet to help you provision your device. Or use the generic template. With that you can definitely register and make calls with an outbound rule you have to configure separately.
Lastly, borrowing an NFR will make your system very unpredictable. That is not a professional solution but moreover, it generates a plethora of issues. It's like the guy that mentioned in a previous thread that this is like a hacked windows. Not only you start to get UI frustrations, but you can be an easy target from a cyber security aspect.