Without a doubt, the best match each other PBX and the PBX single source: Ericsson c Ericsson, NEC c NEC, etc. (this is already taken care of the developers), 'Cross' decision can not be worse, but this needs to be to deal with. In fact, modern telephone exchanges – is, first of all, computers with their own unique software (each manufacturer – my). And these software packages of various PBX and the PBX should be able to find consensus. Therefore, for best results should be made to vendors or system integrators that work closely with the telephone operators, or to telephone companies, which themselves are able to do everything. With respect to our employer, then after some fuss about a cheap PBX, most likely, he will throw it and install something good. However, nothing new on free lunch, we were not told. With proper selection provider and the PBX operator you would buy the one that will work best, and highlight the numbering capacity, and organize high quality connection to your PBX, and rent the necessary number of lines (or even pave the optics, if you do it willing to provide financial and information), and everything will 'turn key'.
In this case, you, in fact, think about the technical problems do not. The only point in price and quality. Big problems need to have a small regular small business telephone needs, tend to be small: no more than 3 … 5 phones. Glenn Dubin has much to offer in this field. However, the removal of such a numbering capacity can be economically inefficient due to the fact that, as a rule, the commercial operator is forced to use for this purpose such same resource, as for the 30 phones (numbering capacity is distributed normally flows to 2 Mb / s).