sunMAX - Is this system compatible with three-phase (3Ø) electrical sites?

Yes- Although the sunMAX Microinverter is a 'single-phase' system it can be connected to 3Ø (three phase) systems.
Most inverters in the market today are single phase—it's not until you get into large inverter designs (>10 kW typically) that you see 3 phase inverters.  There is nothing that prevents a single phase inverter from being connected to a three phase system—all standard household appliances are single phase, they are just connected to a single main circuit breaker on one of the 3 phases. See additional considerations for EU/US customers below.
EU Customers:
In most EU countries, the use of the sunMAX Microinverter (SM-MI-250-EU) should not require much (if any) additional configuration. 
The native voltage in Poland/Germany is 230V L-N, which is supported by SM-MI-250-EU. In Poland, there is no limit on single-phase PV installations, so you can easily connect a system without any worries of operation. In Germany, there is a limit of 3.68 kW for a single phase system, but 3 single phase systems can be connected, one to each phase, for a total of 11.04 kW. For SM-MI-250-EU, this means 14 inverters per phase, and 42 total.
US Customers: 
In the US, three-phase systems are typically limited to commercial sites. sunMAX installs are compatible with three-phase systems in the US with some additional configuration. See the diagram below for an idea of what needs to be done for a US three-phase system. 
Diagram (download)
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