Yes, we all work from home, there is no real office. The PBXnSIP software is hosted on a Linux box in a commercial data center. So this box is actually our company PBX. I have now configured PBXnSIP with 10 trunks (to each of the SIP accounts) and 10 dial plans. Each employee has two identities on the SNOM telephone, one is the account of the central number, the other account is his own account. So each user can choose whether to dial out using the central number (for calling new customers for example) or using his own number. Customers can call the central number or the extension if they know it. Also internal calls, routing etc. works just fine.
The phone company sold us the 10 SIP accounts because we ordered it this way (out of ignorance) but it can be reconfigured to a SIP trunk.
However, having true SIP accounts may not be a bad idea: In case our Linux box fails we could quickly reconfigure our telephones to directly connect with the phone company. So we will not lose connectivity. I think this is a good thing to have and I am not sure whether I should give this up if I can avoid it.
My only problem is whether I have to use 10 trunks since this requires a much more expensive license key.
In Germany (where I am located) most ISPs offer high-speed DSL plus several SIP accounts plus telephony flatrate plus router for small money. I pay about US$50/month for unlimited 16 MBit DSL, unlimited telephony and 8 SIP accounts. So if PBXnSIP would offer the 10 user version with 10 trunks instead of just one, that would be a killer product.