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Update (April 2, 2009 by BigBoss) I just pushed an update to Crash-X’s VoIPover3G v1.0.2 that will enable skype in the plist for you. No need for editing plist files just update the VoIPover3G app.

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Update (April 1, 2009 by BigBoss and ranova): Saurik just released mobilesubstrate 0.9.2805-1. This version fixes the problem entirely allowing for mobilesubstrate addons to work with Skype app. You can now use Skype app with VoIPover3G! -
Quick Tip: The voipover3g string for Skype is: com.skype.skype -All lowercase. You must add it in the VoIPover3G.plist located in /Library/MobileSubstrate/DynamicLibraries/
Full Guide to add Skype to voipover3g

Latest clippy and keyboard custom sounds now also seem to work with Skype using the latest Mobile Substrate update. If you are still experiencing crashes when you open up the keyboard, disable these two components.

If you are still experiencing crashes with the new Mobile Substrate and have disabled clippy and\or custom keyboard sounds, make sure to check other mobile substrate extensions or apps that run in the background and disable them. They may be still conflicting with how Skype runs. This is not a Mobile Substrate problem, but a problem with the extension or app itself and the author of it will have to update it. I had no problems using Clippy, Cydelete, Cyntact, Five Icon Dock, QuickGold, SBSettings, VoIPover3G, and Winterboard as mobile substrate extensions.

Known extensions or apps that cause skype to crash: mcoolphone, mobilelog, AdvLock, Hood, and Intelliscreen (it may work if you mess around with the performance settings in Intelliscreen).
You can check what mobileSubstrates extensions you have running and installed by looking in the folder:
/Library/MobileSubstrate/DynamicLibraries/

If you use Intelliscreen, From User Daron:

Eventually, I discovered that Skype would launch if I *disabled* IntelliScreen. I then tried to disable some of the IntelliScreen Performance extensions (Backgrounder, FileSchemaMobileSafari, MailToAttachmentMessageUI, PrefHooker-iKeyEx, SBHooker-iKeyEx, SBSettings, Veency, VoIPover3G, WinterBoard) and discovered that the culprit was Veency.

Thank you Saurik and everyone else that posted comments that helped us figure out the underlying problems.
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Update (March 31st, 2009): Saurik has released a new mobile substrate and the issue is fixed. No need for intelliscreen or any other hacks. Just update mobile substrate from cydia. Update to v0.9.2803-1 (or newer) of mobile substrate.

To fix the Skype crash, all mobilesubstrate based hacks are disabled on the Skype app. This means you cannot use voipover3g or backgrounder with Skype app. Do not ask how to do it or point out that it doesnt work. The developer of mobile substrate has already stated that it will not work.

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The highly anticipated app for the iPhone has just been released in the US:
Skype in the AppStore.

Now the bad news. It seems that all jailbroken phones do not play well with the Skype app. I had problems getting it to work at all, the app would crash when you try to use the keyboard to login to the app. I later found out, through trial and error, the culprit for keyboard crashing is Custom Winterboard Keyboard Click Sounds and Clippy. Getting rid of the keyboard custom clicks (tock.aiff) seems to work with regular themes. Using SBSettings Clippy toggle to switch it off seemed to do the trick also.

That problem, while small and fixable, is not the biggest problem. Skype seems to freeze within 30-50 seconds while in the app – no matter what you do (calling, idling, chatting, etc). I went into safe mode using SBSettings and tried out Skype – to my surprise, everything worked perfectly – I used it to talk to my friend for about 20-30 minutes. I decided to do a little bit more troubleshooting – deleting mobile substrates one by one to see if it helped or not, and then deleting them all. Nothing seemed to work, the app would still crash within one minute.

I decided to run SysInfoPro and compare running processes (non-mobile substrate) between safe mode and regular mode. They both had the exact processes running at the same time.

Although I didn’t delve much deeper into the problem (could have tried using Top and system logs), I have come to a conclusion that Skype crashes ONLY on jailbroken iPhones. I had a couple friends try it on their newly restored iPhones, and they worked flawlessly. Other people from multiple forums have also said it crashes non-stop for them (their iPhones also jailbroken):

“I managed to download skype and tested myself. It is buggy and all the symptoms the same as described by ranova. I have tried it on a 1G phone newly updated to 2.2.1 jailbroken. The only apps I have installed is sbsettings, ierase, nimbuzz, and skype. It still crashes after 30sec or so. It has got to be the phone that is jailbroken. I have nothing on my phone other than what you get after you jailbreak.” – duceduc

“2.2.1 jailbroken 3g here. It crashes after 30 – 60 seconds.” – jgsx

“Confirmed – Crashes like every minute.” – Zazox

Let’s hope this isn’t an attempt from Apple or Skype to cause apps to crash only on jailbroken phones (to deter the use of voipover3g). [end conspiracy theories]
Update: Saurik has just updated regarding reasons behind the crashes:

“Skype seems to be using some kind of /awesome/ DRM that involves them having an entire replacement binary somehow inside of it: the one on disk doesn’t link against /anything/ ;P. Whatever its doing, though, involves stressing dyld in some weird way.

Interestingly enough, its not anything MobileSubstrate does to the code: its just it existing in the process before it loads its replacement. (Which is extra weird, as the new MobileSubstrate links against almost nothing: just CoreFoundation.)”

So what we know so far:

• If Skype crashes when trying to input text: Disable both clippy (Use SBSettings toggle) and any custom Winterboard sounds relating to the keyboard tick (tock.aiff).
• If Skype crashes within 1 minute of having the app open: Update your Mobile substrate via Cydia. The latest version (April 1st, 2009) allows mobile substrate to play nicely with Skype. Thanks Saurik!

Temporary fix that allows mobile substrates extensions (voipover3g, backgrounder, winterboard) to run, from Autotrade at Engadget:

“For people having crashes (especially the 1 minute thing) use this FIX: I had to enable in Intelliscreen, Performance, App Boost ON and select the apps below (in my case I set Backgrounder and VoipOver3G both to ON). That fixed it, no more crashes at all, tested this on 2 iPhones.”

Well there you have it, Skype on the iPhone is amazing – sound quality sounds better than regular cell calls. I briefly tested it on T-mobile’s EDGE network (using voipover3g) and for the 30 seconds that it lasted, there was no noticable lag and quality was great! I look forward in using Skype as a regular VoIP app. Thanks for all the comments and thank you saurik for looking into this.