Phase 1: Services
Getting A Dialtone on your Batphone
Before you choose a calling app, device, or prepaid phone, you need to choose a calling service. The service you pick will determine the hardware and software options that you have available to you. Choosing a service will depend first and foremost on how you plan on using your batphone.
If you don't plan on using your batphone while on the move, an Internet phone service may be best. Even if you do plan on moving around, Internet telephony might still work for you provided that you have access to the Internet most of the time. If you plan on moving around a lot, or if you just aren't sure about Internet access, a prepaid mobile might be a better choice for you.
Batphone via Internet
There are a number of applications and services available for placing voice calls over the Internet, each with its own strengths and weaknesses. Rather than publish an exhaustive list, I will list the ones that I use on a regular basis and have some experience with in the Internet Telephony Service section of this site. I am neither affiliated with these services in any way, nor am I being compensated by these services in any way.
If you want to avoid Internet calling and use a mobile phone with a prepaid mobile service, you can read about prepaid service in the Prepaid Mobile Service section of this site. Again, I'm only going to talk about the mobile services that I have experience with. I'm not affiliated with them and I'm not advertising for them.
Whether you want to use Internet telephony, or a prepaid mobile, your batphone experience can be greatly enhanced with Google Voice. GV is available to anyone in the U.S. with a Gmail or Google Apps account. GV provides you with a telephone number that any PSTN phone can call and that any mobile phone can send text messages to. Calls and texts to your GV number can be answered on your computer, or forwarded to one or more numbers of your choosing.
You can add multiple PSTN numbers for GV to ring on an incoming call, such as a mobile phone, home phone, or an office phone. The first line to pickup gets the call, so make sure that any line that you add doesn't go to voicemail for at least 45 seconds.
GV makes a distinction between mobile phones and home or work phones. Two GV accounts can have the same home or work phone numbers added. Conversely, only a single mobile number can be added to GV, but you can also set that number to also receive SMS messages that are sent to your GV number. If GV forwards an SMS to your mobile and you use your mobile to reply to that message, the message will have your GV number associated with it, rather than your mobile number. This is handy when using GV with a batburner. Getting your contacts set up to work can be a little involved since the sender numbers in Google Voice can look weird under some circumstances, but you will probably not have many contacts on a phone line dedicated to a specific purpose.
GV can't actually tell if the line is a mobile, land line, or VOIP service. You get to select that option when you register the number with GV and you can change the designation at any time. Once a phone number is set up with GV, you can temporarily disable it by simply unchecking the box next to it. This is handy if you have multiple phones set up, but you don't want all of them ringing at the same time. This is also better than using a mobile service provider's call forwarding because you do not need access to the phone to enable or disable forwarding.
Various applications and services pop up from time to time offering access to GV in some novel way, but they don't stick around for long. You will get the most reliable service from GV using call forwarding to a PSTN number. Any other method is subject to change. YOU HAVE BEEN WARNED!