Siphon SIP App for iPhone Works over AT&T's 3G network? Holy Toledo!

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Siphon SIP App for iPhone Works over AT&T's 3G network? Holy Toledo!

itexpo09.gif I tested Siphon, a SIP-based VoIP application for the iPhone, in California at ITEXPO. Interestingly, Siphon worked perfectly in California over AT&T's 3G data network. Yes, you read that right - VoIP over 3G! I couldn't contain my giddiness when I realized I could now register my iPhone with TMC's Asterisk-based IP-PBX and make/receive calls. I've tried Siphon a few times in the past and it never worked over 3G - only WiFi. I thought perhaps AT&T was now easy their restrictions and allowing it. (silly me)

However, once back in Connecticut I tested it again and it didn't work. Apparently, in some parts of the country AT&T is blocking port 5060, the default SIP port. I did some port testing on my iPhone and indeed AT&T is blocking outbound port 5060. While I was in Los Angeles I was able to use Siphone to make & receive VoIP calls over the 3G data connection through my corporate Asterisk-based PBX. I was able to receive calls to my TMC extension as well. Guess it was good while it lasted...

Now, Siphon does let you change the local SIP port from the default 5060. In theory, the Siphon application can be modified to use a different outbound port and then you could setup some port forwarding rules on your firewall, i.e. map the 'always open' port 80 (web) on your firewall to forward to port 5060 when connecting to your SIP-based IP-PBX's IP address. Or if you IP-PBX is already using port 80, there are plenty of other outbound ports that AT&T doesn't block.

Apple has rejected and blocked Siphon from the App Store. Interestingly, Apple allows other SIP clients (WiFi-only) to be downloaded from the App Store, including iPico, fring, iSip (supports push notifications of calls), Acrobits Softphone, WeePhone SIP, and Nimbuzz. What's interesting about the Siphon app is the whole saga the developer had to go through with Apple when submitting this SIP application to the App Store. It wasn't pretty...

The short story is that even when Siphon didn't support VoIP over 3G a few versions ago, Apple still rejected the app providing a lame excuse. Then after several attempts, Siphon went "underground" and provided their SIP app to Cydia, the primary jailbroken app store - with full VoIP over 3G functionality. If you can't beat em', screw em'! That's why a lot of apps have gone to the Cydia App Store to get around Apple's ridiculous restrictions.

Check out this screenshot of my iPhone showing how you can enable Siphon over EDGE/3G:


Unfortunately, like I said earlier, AT&T is blocking outbound port 5060 in some parts of the country, so simply enabling Siphon over Edge/3G by itself won't work if they block it. Apparently, the AT&T cellular network in Los Angeles, California works though. If anyone else has gotten Siphon to work over the AT&T 3G network, post a comment - or even if it didn't work. Would be a good gauge of how widespread they allow/disallow this.

The day is coming when the carriers will have to allow VoIP over 3G. Look at what VoIP, and especially Vonage did to the traditional landline industry. We went from paying long distance minutes by the minute to an UNLIMITED plan with UNLIMITED minutes for a flat rate. The mobile industry will soon have to follow suit.

In fact, the first wireless carrier that lets me register my cell phone to my SIP-based IP-PBX over a 3G data connection will become my new wireless service provider and have my business. I'm sure millions of others feel the same. Heck, charge me a few cents for terminating or originating my SIP-based calls. I'd pay for the ability to use my corporate identity (CallerID) when making business calls on my personal cell phone. Or just count SIP calls as 1.5x or 2x per minute of usage towards my current monthly plan's bucket of minutes. Of course, the carriers would have to detect when a SIP call originates or terminates, which is a technical challenge. They'd have to do packet inspection on a mass scale to support this.

Still, there has to be an appropriate revenue-generating business model for the wireless carriers that will allow their customers to use SIP over 3G. Make it $5/month extra or something. Vonage took the traditional landline providers by surprise, causing the defection of millions of users. So if the wireless carriers wait too long, some new wireless carrier is going to come along and do the same by offering VoIP/SIP over 3G. You mark my words...

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Hello Mr Keating,

I have read your VoIP / SIP over AT&T's 3G post a few times over the past couple of weeks.

Which version of Apple's iPhone are you using, 3G 3GS?

Additionally, which version of siphon are you using?
Did you modify and build the siphon app or did you d/l
the bits from the developer's Google site?

I have been complaining for decades about Telecoms impeding technology to squeeze every last cent out of consumers. Yes, I know its their network and they will do as they please with it (within FCC regs).

When will ISPs provide telephony over WiMax!?!

Best Regards,

Mr. Keating,

As of this post, I can confirm that the French cellular carrier, Orange has not blocked port 5060 for the Siphon application. Therefore, when you are on business in Paris SIP over E/3G is possible.


I use a new service that is being released soon in the US direct sales industry, where you can make SIP based calls over the WCDMA and CDMA 3G networks in the US. I am using the service over AT&T network and have not had any blocking problems. Also I am an Engineer in the Wireless industry and I can tell you that they are not blocking this port in the DFW area.

Phil S

There is a way around these restrictions that is free from cydia.3g unrestrictor, is a paid app from the cydia app store that tricks your iphone into thinking that you are connected to wifi and thus allowing you to make calls over your cell network.However, if you install the sinful iphone repo, 3g unrestrictor is available for free from them.The repo is
To add a source in cydia select manage>Sources>Edit>Add, then type repo above, wait for load and then install 3g urestrictor(which is all the way at the bottom of the sinful packages list.)

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