I just want to clarify that usually if you wear a streamer around your neck (which you can just tuck under your shirt) then it should usually work with either iPhone or Android phones. You don’t need to shell out money for an iPhone if you already have an Android phone with Bluetooth. And the streamer may have a mic built in to it so you can leave your phone in your pocket and just hit a button on the streamer to answer phone calls. Or the streamer may need a mic clip attached to it. Basically the streamer is the interface between your phone and your HAs.
If you want to avoid this streamer interface, there are a few brands/models that now support direct streaming from iPhones (or iPads, iPods, etc) to your HAs directly, without going through a streamer. But as far as I know, this setup only works with iPhones right now and not Android phones. That is because the Apple already has a proprietary Bluetooth Low Energy protocol on their iPhones that the HA mfgs use to enable direct streaming. Eventually when there’s a Bluetooth Low Energy standard created and adopted by Android phones (and even Apple iPhones), then HA mfgs will be able to use it for direct streaming with all phones. But the bottom line is that you’ll need to buy an iPhone at the current time, along with an HA that supports direct streaming to iPhones, if direct streaming is what you want.
Direct streaming is nice but not all that convenient because it’s only for listening and you still need to pick up the phone and answer it and hold the phone’s mic up near your mouth for talking. With a streamer worn around your neck, especially if there’s a built-in mic in it already, then you can leave your phone in your pocket and just answer the phone by clicking a button on your streamer and carry on your conversation with the phone in your pocket.
As for your concern about HA battery life due to Bluetooth connection all day (in the case of direct streaming), this shouldn’t be a big concern because direct streaming doesn’t use regular Bluetooth connection. It uses Bluetooth Low Energy instead, which uses much less power than regular Bluetooth. Sure, it may still affect battery life somewhat if you use direct streaming a lot, but you should still be able to get about 4-5 days of battery life which is reasonably good enough for the convenience.