phone, What is sip and how to use it, applications review

q What is Sip?
a Sip is protocol for telephony over internet. 
Similar to e-mail protocol, or sms. You can use any program for e-mail, or any phone for sending sms.
Also you choose your e-mail provider, the same way you can decide to use gmail/yahoo/microsoft, whichever you want to use.

q Can I make phonecalls using sip
a Yes.
a Longer answer: Yes, you can call other users using apps with same protocol (sip). Call is made using wifi/mobile interenet.

q Can I call people who do not have (any) sip app installed?
a Some providers offer rates for calls to landline/mobile phones, which are usually much cheaper then telecom providers.
Call to landlines are cheaper than call to mobile. This rates change from time to time.
More info in another file, soon (voip providers review.)

q Can I send messages using sip
a Yes. There is a protocol caled 'simple' that supports sending messages.

q Which programs can I use

app name	platform	portable	voice (sip)	msg (simple)	size	app licence	multi accounts	internet web address of prog
microsip	windows os	supported	supported	supported	4mb	open source	yes, 1 at time
phonerlite	windows os	supported	supported	supported	5mb	freeware	yes, 1 at time
csipsimple	android os	apk available	supported	supported	9mb	open source	yes, parallel
linphone	android os,win	play store	supported	supported	14mb	open source	yes, parallel, supports video too.

yes, 1 at time: you can setup more accounts, but people can just send you message/call you on the one currently selected
yes, parallel: you can setup more accounts, people can send you message/call you on any of the already set-up accounts.
2, parallel: you can add 2 accounts in total. people can send you message/call you on any of the already set-up accounts.
There are others apps for android and iPhone too. (I haven't tested iPhone apps.) Some have problems with connection (sipdroid.)
Most other apps are are bigger. (More info in other file, soon.)

q How is that different from Skype or Viber, or Whats App?
a You choose your sip provider. Example: linphone, iptel, ippi...
You get to choose which app you want to use, preferrably open source or freeware. 
They don't have ads. (At least for now, hopefully never will.)
If you don't like the program, if it's to big, or does not work properly you can change it. 
Try that using skype or viber.
If you don't like your provider, change it. You can still use the same app, and call other users. (Your username/address will change, though)

q Can I call between different providers (linphone, ippi, iptel)?
a Yes. Most of these do allow free calls between them. 

q Can I call using different programs (csipsimple, phonerlite, sipdroid)?
a Yes. They use the same protocols. Sip for voice, simple for messaging.
(Note: There are other protocols that aim at the same area, such as xmpp for messaging, and jingle for voice protocols.
Some programs support both xmpp/jingle and sip/simple protocols, such as Jitsi program.
If a program supports just sip protocol you cannot make call to program that supports jingle protocol.)

q Which protocol for voice should I choose?
a Sip is well known. Android 5 supports it directly from phone dialer. Xiaomi phones too.

q Which protocols are there:
sip - audio and video
simple - messaging, extension of sip
xmpp - messaging
jingle - audio, extension of xmpp
webrtc - communication using web browser. audio, video, text. (sip is sometimes used inside.)
iax - mostly audio, and sometimes video, somewhat similar to sip. Uses just one port. Sip uses 2. System resources usage?
proprietary (skype, whatsapp, viber)

q What about secure calls and messages (encription)?
a see here:, 
	CSipSimple (sip encrypted protocol, 
	redphone (username is phone number) (open source protocol, not sip)
	chatsecure (xmpp protocol)
	textsecure (data messages are encrypted, sms/mms are not) (open source protocol, not sip)
But, I would not put too much fate in encryption online :)

q is there open source free app that uses phone number as id, like Viber or Whatsapp
a Yes. Redphone
The thing is, to see who else are using the program, developers usually have to have database with user's phone numbers.
Redphone does not use sip protocol, btw.

Alternative is to register another username in the form of your phone number. like
And give that number to your friends.
But people remember other people usernames easier than phone number.

Bonus questions:
q Can I use landline phone, over sip protocol, to dial another number
a Some providers support hardware devices. If your adsl router has phone port, not lan port, usually marked voip, you could try.
Set up voip account in the router, and plugin phone in the router. 
Try dialing your mobile phone, and see caller id. It should be something like, or something similar.
Also your phone line should is free at that moment.
Meaning you are using voice over internet, and not landline to make calls.
If you connect 2 phones to 2 different routers in 2 different houses, you can dial inum from one house to another.

q Can I use landline phone, over sip protocol, to dial another sip user
a some sip providers give you (free) inum number. They start with +(883).
Example: ippi, localphone (you have to ask for inum number, it's free).
So you could dial from landline phone inum number, using just numbers dialpad.
Inum numbers are 15 digits long. Speed dial could be useful :)

q Can I dial from inum to fixed landline for free.

q Can I dial from sip to Viber.
N No but you can dial from Viber to INUM. (You get free inum phone number, when you oppen account at 
Some other providers offer free inum too.)

q What is open source
Anyone can see how to program works, change it and compile it oneself. Also make another version oneself.
Like recipes for meals.
Also if programer abandons program, and the source is available, someone else can continue the project.

q Why describe this programs
a Open source/free, small and portable programs have preference in testing.

q Any other usable programs
a Jitsi is good on Windows. You can probably delete java that comes with it, if you already have java installed.
It supports multiple protocols, sip and xmpp.
There are many other programs on android. Eve sip on android is ok, but it keeps asking you to buy video part. 
I did not test bigger downloads.

More info:

redphone and textsecure protocols: