Scala Rider G4, is a full A2DP system that stupport mulit-connections and alows you to switch between them.
Scala Rider
All of the latest generation BT headsets support A2DP and AVRCP (remote control) and they all allow you to switch between connections. The advertising B.S. will have you believe that you can call the moon, but you need to dig deeper to really understand what they can and can't do. When they say they can pair up to 8 devices (Interphone F4) that doesn't mean they can be connected to 8 devices. It just means they memorize 8 device IDs and connect to them automatically when there is an open channel and they are within range. A phone's BT ID will usually prevent it from pairing on a low priority A2DP channel, but some phones will consume the A2DP channel in addition to the high priority hands-free channel, leaving you with no other connection options except for the wired aux jack. Some GPS use headset profile and some use A2DP (stereo headset) profile. Some headsets like the XBi2 allow a GPS BT ID to connect to a low priority channel and others like BT2 do not. Each one has different limitations, they don't all work as expected with all devices, and not all device combinations are guaranteed to work. If you just read the box and don't understand the limitations beforehand you may be very disappointed.
The Scala Rider G4 has 4 bluetooth channels. It has one high priority channel for phone
or GPS, two medium priority intercom channels to connect to other Scala Riders, and one low priority A2DP channel. The only way to connect a phone and a GPS is to pair the phone to the GPS using the Handsfree profile, then pair the GPS to the G4. This is a direct quote from the Scala Rider G4 manual:
"NOTE: If you plan to use your mobile phone while using a Bluetooth GPS
device, then you should pair your mobile phone to the GPS and
not to the G4 headset."
The BlueAnt Interphone F4 has one high priority channel for phone, one intercom channel which also supports hand-free profile and allows connecting to a phone, and one low priority A2DP channel. If you connect two phones (or a phone and a GPS) then you cannot use the intercom. From the F4 manual:
"GPS NAVIGATORS use the TELEPHONE (headset) profile for
audio connection: to use a telephone whilst using a navigator,
you will need to use the specific function of the GPS
device."
and...
"In telephones equipped with musical players, and therefore which
include a Stereo (A2DP) profile, the Telephone + Stereo (A2DP) function
coincides. As such, it may not be possible to connect a further Stereo
(A2DP) player."
The Midland BT2 has one high priority channel, one intercom, and one low priority A2DP channel.
"If you pair the BT2 unit with a GPS Sat-Nav, you will not be
able to pair it with a mobile phone, because both these devices
are assigned (high) priority 1.
This problem can be easily solved by pairing the cell phone
directly with the GPS Sat-Nav and by then pairing your GPS
with the Midland BT2. In this case, the cell phone features will
be managed by the GPS Sat-Nav."
The Sena SMH 10 manual is unclear about the number of channels it has available, and how it prioritizes multiple pairings.
The Chatterbox XBi2 has one hands-free channel (phone), two intercom channels, and one A2DP channel (MP3, GPS, radar) according to their manual.
Those are the ones I've researched. I think they are the top choices on the market right now. None of them have replaceable batteries.