I am going to a foreign country for a trip in a few week. To save on roaming fees I want to call my friends at home with VOIP. However, I don't want to call real phone numbers by buying a service from a VOIP operator but cal other SIP accounts for free, for example Linphone account->Linphone account from my Android mobile phone and tablet and Slackware netbook. I tried to make a call using 2 Linphone accounts but the voice delay is noticeable. Sometimes it looks like there is voice no delay but a bit later a delay is like 1 second. For testing purposes I made a usual call with two mobile phones in the same room and there was no delay at all. Can you recommend the best free SIP operator you ever used or should I just accept voice delay? I like Linphone because their software is open source and they have a command line client.

There will always be a delay just because that is the way VOIP works.
You will not notice any delays when you devices are not next to one another.
Test it out with your friends and you will see it's OK.

In your experience, can free SIP VOIP account be as reliable as a normal mobile phone call in terms of latency?
I don't understand why I wouldn't notice any delay if devices weren't next to each other? In my tests they were connected to different networks - one of them was connected to my Wifi network and the other was using my carrier mobile data plan yet latency was still there.

I remember that about 2 years ago I called my bank it Poland from South Korea using a paid SIP account and that it worked well enough for both sides to understand each other but I can't say whether I experienced any voice latency but it was when I realized that there is a big power in VOIP.

I don't know as I have never used one of them.

The only reason you noticed this is because you can hear both ends of the conversation. Once you remove one end you will not notice as much as you think you.

And the same will apply here. I call Germany on a regular basis and have no issues. I use 007Voip. It is a pay as you go service.

I just asked someone in another room to pick up Linphone call and delay was still there. And the usual phone call made with two phones put next to each other on the table involves no voice delay. I am quite sure that a voice delay would still be there even if two ends were far away from each other and it's a shame.
What country did you call Germany from?

In VIOP there is always going to be a delay you cannot get away from it. Payed for or not. HANGUP the cell phone and use the linphone only. You are not going to detect the delay when you cannot hear the other end. If you cannot live with the delay then use a land line.

I call from USA.

Actually, all telephone connections these days use IP in one form or another. If you are talking overseas even on a "pick up the phone and call" connection, delays and latency can occur. You'll hear it as though the person speaking was taking a moment to think about what s/he wants to say. Don't worry about it: you're calling someone for free.

I am actually going to use Linphone on my cell phone I just checked that ping to sip.linphone.org takes ~41 ms from where I live. Local VOIP providers provide VOIP service with ping ~8 ms. It's 4 times less so I might give it a try and see whether it helps. When I will be away from my home at least one side may suffer less.

There are a lot of things at play here too. Network quality at the location you will be traveling to will always play a part.

I talk with my sister on the other side of the planet on Skype. It works pretty good really. A slight delay but not bad at all.

I guy at work went to El Salvador. He bought a magicjack and it worked well he said. A bit of time delay is common. It will be on any phone over that distance.

He also used a republic wireless plan on the $5 and it worked great too he said.

I've used the free app from magicjack on android. It works OK for free.

These are all typical phones.

Today I called someone several times using Linphone account with Android CSipSimple app on mobile internet connection instead on WiFi. I didn't notice a voice delay being more serious than when I was on WiFi although connection speed was definitely slower. Good point is that the connection was stable. So at the end of the day I think that, as everyone in thread said, a voice is delay is inevitable using SIP. Thank everyone for their replies. I am marking this thread as SOLVED.

I use GrooVeIP and the cost is $5.00 from the google play store. Their VOIP provider is RingTo.

For a one time payment of $5, you get to make and receive free calls to landlines and mobile phones via wifi and/or your 3G/4G data plan. You also get a free DID number, aka a phone number. There is NO FEE or monthly charges for the DID number.

The setup is easy. Everything is done in the GrooVe IP app, you setup an account and a choose a free DID number and that's it.

The voice quality is good at least in my experience. Also, if you have a QoS ( Quality of Service ) settings in your router this can improve your VOIP calls.

The only downside is it doesn't do SMS yet.

I'm sorry average_user for not reading your post carefully. All I did was a fast skimming.

The above method is to receive and call real phone numbers via wifi. However, you wanted to call sip accounts via wifu. Using a Linphone account and the android CSipSimple app is an excellent choice.