Nexus 4 and 5 have their UART via the headphone jack - you need a TRRS headphone cable with the correct resistor wired up to one of the pins.
Kenwood even came up with a standard for it: http://www.miklor.com/COM/UV_Technical.php#progcable
A popular series of VHF/UHF
var header = sampleRate; // 1 sec to charge/discharge the cap
var bufferSize = samplesPerByte*data.length/*samples*/ + header*2;
To top it off, he uses 2 stop bits. The signalling rate may be 9600 baud but do not expect to be transmitting 9600 DATA bits a second! I think such claims need to be backed up with a demonstration full loopback capability without either side dropping a byte, with no pauses between serial bits.
I could probably get away with 1 stop bit... I didn't try. To be honest if the transfer speed matters so much, it might be better to use some other means of communications :)
I've always been bothered by Apple and the other tablet maker's choice not to include an openly usable simple serial port on their devices (or the ability to use a USB<->serial adapter). I understand the Apple "control everything" mentality. Their sandbox, their rules. Still, I can only imagine how neat it would be if all of these devices had a simple two wire serial port available without limitations. As a result of this we have to go backwards in technology by some 30+ years for simple little projects.
I assume you mean android and not microsoft phone or something.
I use these for BT with android and an arduino mini. And some other devices.
http://www.adafruit.com/product/1588
aka the famous $20 Bluefruit EZ-Link
On the android side I use an app called blueterm once I connect. Its pretty boring, it just does its thing. I would imagine writing an app on the android side that does something useful and gets it on the tablet would be quite a challenge. So the BT link itself is not really the limiting factor.
Ironically in an article about programming devices, there is some weird funkiness with linux and various desktop environments and OSes such that its non trivial to wirelessly reprogram arduinos, something about toggling the DTR at the right speed and time, although the RX/TX work just fine.
I have no extensively experimented with range.
Looking at "radio shack type price markups" I think a DB-9 and hood and some cable would be a significant fraction of $20, its not like we're comparing a 5 cent solution to $20, more like $7 wired vs $20 bluetooth. On the other hand it bothers me a little to connect a $20 BT dongle to a $15 mini.
> Still, I can only imagine how neat it would be if all of these devices had a simple two wire serial port available without limitations.
Whatever the device or manufacturer, why compromise the design to include something which almost no one will ever care about, much less use?
http://www.slideshare.net/Sudar/transfering-data-using-audio...