This can be very important when each SIP account represents a different company/business. Although one person is dealing with all those businesses, when an outgoing call is made it is imperative that the correct SIP account is used to make that call so that the recipient is correctly informed who is making the call.
So really, your issue is with presented identity in terms of caller ID name and number then? Can you set outgoing caller ID name nad number on the 6 provider accounts? If you can, you may have some better options. On our platform, we use the dialplan to route all calls to the most appropriate provider, based on the number that was dialed, and what the rates are for each carrier in a given area (least cost routing), although reliability in certain areas is also factored. Each extension registers with a single registration, and has it's own internal caller ID name and number (the user's name and extension). We use the Aastra phones, and built a little XML app that lets the user pick from a list of possible caller ID name and number combinations. This tool updates the database value that will be used for effective_caller_id name and number. With this setup, one user (one SIP registration) can have an unlimited number "businesses". For incoming calls, we prefix the caller ID name with a short string that identifies the incoming number or "business". Sometimes, a combination of registrations and the selector tool is best. If you don't have XML browsers on the phone, you could just as easily do this with an IVR tool, a web page, or with prefixes. Whatever is easiest. You can have more than one option. If your upstream providers can give you DID numbers, you can have more than one business on the same provider account, which is a lot easier to manage (one gateway entry, but lots of "lines"). This is getting into serious PBX stuff though, and I get the impression you don't really want a PBX. Or do you? -Tim