Develop Reference

Lowest Android Version Possible For SNMP and PPTP

I'm having to create a new app for our installers and they currently have an app that they use on Android 5.1. It doesn't use either features mentioned in the title but I'm looking to implement that in the new app. I'm just curious what version do the new phones need at minimum to support an app that allows for both of those to be supported.
SNMP is going to be used to make calls to subscriber modules. Itll have to be able to use both Version 1 and Version 2. It'll be completely equipment based.
The PPTP connection will be only for the app itself. I don't want it to default all traffic the phone is using to that connection. Merely only what calls the app makes to the network. Is this even possible?

PPTP
I'd have to assume there are libraries out there for version of Android that didn't include it natively, it looks like v4.0 is the earliest Android version to include PPTP.
"Android includes a built-in (PPTP and L2TP/IPSec) VPN client, which is sometimes called legacy VPN. Android 4.0 (API Level 14)"
https://developer.android.com/guide/topics/connectivity/vpn
SNMP
The best thing I can find for SNMP is an app that uses SNMP on Android 2.3.3. Who knows what library or home-rolled code they used to do it, but it looks like you have some "wiggle room" if you're just needing it for Android v5.x.
https://snmp-agent-4a.en.aptoide.com/
Another link that shows the age of SNMP on Android doesn't say what OS version it's talking about, but we can see the images are of fairly ancient phones. It's circumstantial at best, but it looks promising for your project.
https://www.dpstele.com/snmp/monitoring-smartphone-best-practices.php

How to build my pure Java (Swing) apps for Android 5.0?

The Android 5.0 page states that 'Pure Java language apps run as 64-bit apps automatically'. I cannot find any documentation on how to configure/build my java apps for Android 5.0. Has anybody had any success with this yet?

You're misinterpreting what they meant: they meant that Android applications without an NDK component built in C/C++ (i.e., built entirely on the Java based Android SDK) will automatically be compatible with 64 bit processor devices, not that desktop/Swing Java apps will run on Android devices.

Mobile phones supporting Java Android?

What are mobile phones supporting Java Android?
Is there any Nokia phone supporting this technology?
What should the mobile contain (a framework, a plugin.. etc) if we want to deploy a Java Android Application?

Android can be deployed to many devices with custom builds of the OS; anyone can build Android . It is not limited to particular handset makers and you might want to consult the makers for official lists of deployed devices.
There is nothing the device needs to contain (other then an appropriate targeted version of Andrdoid) to deploy an application.
One important note is that the application IS NOT run in the JVM, the code is only written in Java and then converted to Dalvik bytecode when compiling (Android runs on the Dalvik Virtual Machine). Since the code is written in Java though you can make extensive use of existing libraries and use them in your applications.

There is a fairly comprehensive list on Wikipedia comparing devices running Android, including forthcoming devices.
Nokia seems to have no interest using Android platform for its devices.
If the device is a certified Android platform, there is nothing one needs to add for deployment.

I think most phones that run Android should support Android applications. However, IMHO one would be hard pressed to compile a list of those phone.But rest assured, it's a lot. Someone DID make a list! And yep, it's a lot.
Some quick Googling reveal that Nokia seems to not like Android so I would assume there is not a Nokia phone with Android.
Framework: Eclipse Galileo with the ADT plugin
My advice:
read this site inside and out! http://developer.android.com/index.html
It answers all your questions.

What are the differences between J2ME Wireless Toolkits and which one to choose?

I already know the differences between Java Edititions (ME, SE, EE), the ME Configurations (CDC and CLDC), Profiles (like MIDP), and additional APIs specified by JSRs.
But I am totally clueless about the differeces of the several Wireless Toolkits.
For example, Mobile Tools for Eclipse explicitly supports these ones, and states that others exist, too:
Sun Wireless Toolkits
MOTODEV SDK for JavaME
Nokia SDK S40/S60
Sony Ericsson J2ME SDK
Sprint PCS Wireless Toolkit for Java
Siemens SMTK for Series 60
mpowerplayer
Microemulator
I want to develop a MIDP application that runs on as many devices as possible, and I am going to use Antenna for build automation. Anyway, I have to install one or more of the toolkits, but don't know which.
So there are these sub-questions:
What are the differences?
Is there any single one which is the best?
Or do I need to install several / all of them?
I have a Sony Ericsson Device for testing, does this nessecarily mean I need the Sony Erricson J2ME SDK?

The device specific toolkits generally just contain debugging tools and emulators, transfer programs and custom libraries (ie, device specific audio libraries).
Generic midp code should be compatible with all devices, especially Sony Ericssons
I find it is usually audio code which facilitates a need for device SDKs. Nokia also used to use a special kind of canvas but this will only be applicable for really old phones.
EDIT: generally, install an SDK if you need it for something, otherwise use Sun WTK

Each toolkit provides the base CLDC/MIDP classes that are required. In some cases they will be specific to a device, e.g. if you choose the Nokia S60 3rd Edition FP1 toolkit (which I have used) it will use CLDC 1.1 and MIDP 2.0. In addition to this you will find that each vendor specific toolkit will come with added extras that will only be available on certain devices. Since you are looking to write for as many devices as possible you will not be using these extras and should therefore probably stick to the Sun WTK.
When building with Antenna you can specifiy which CLDC and MIDP versions you want to use if you use the Sun WTK too. If you use any other toolkit you might have problems with Antenna because it looks for very specific files (which are hard coded) so if you sepcify your WTK.home variable as Nokia S60 it won't find the files it needs so you will need to do some hacking (all of the class files for Nokia S60 are packaged in 1 jar file, unlike Sun WTK which has them all separated into the JSRs).

I find the Sony toolkit the easiest to use, mainly because it has standard size screens (ie 176x220 and 240x320) that are easily switched between on the emulator
If you are using Antenna to build you applications you should only need to install the WTK and a Blackberry SDK to get a complete set of builds, unless you are going to use device specific apis

Symbol SPT-1800 Java Barcode Scanner

Does anybody know if its possible to write a barcode scanning application for the SPT-1800 in Java?
I don't know how to program the Old School Palm OS.. so java would be great.

It looks like you will have to write a Palm app in C to control that model.
See the Software Development Kit (SDK), v. 4.10 and FAQ: Where Can I find the Palm SDK & Development Tool? for more information.
The Motorola/Symbol sites are not very intuitive so here's a link to all of the SPT1800 support documents.
The SDK's are usually very good and get you up and running with a sample application pretty quickly.
I had hoped to use Java for the MC3000 and MC9000 series recently but it appears Motorola/Symbol has stopped releasing updated Java SDK's for those devices and are concentrating on the .NET SDK now.
The Java SDK's also require additional licensing of the JVM from 3rd party vendors which considerably adds to the final cost of deployment.

I would think that Waba/SuperWaba would be your best bet for an older PalmOS device.