VoIP Bug in iOS 4.2 Golden Master

According to MacRumors, Toktumi the company behind the well-known VoIP application Line2 for iPhone, iPod touch and iPad has sent an email to its users warning them from upgrading to iOS 4.2 due to a new bug founded in this version which results in the ringer continuing to ring even after a call is answered when Line2 is running in the background.

Attention all Line2 iPhone, iPod Touch, and iPad users:

Please do not upgrade to iOS version 4.2.

If you upgrade to iOS 4.2 and you are running Line2 in the background, the ringer will continue to ring even after an incoming call is answered. This affects Line2 as well as all other VoIP and social calling apps. (Note: If you do not use Line2 your Toktumi service will not be effected.)

Apple Developer Support is aware of this issue and has designated its status as 'severe'. However, as of the most recent iOS beta (GMSeed build), this issue is still not resolved. We apologize for this inconvenience and will update you as soon as we get more information from Apple.

Line2 will continue to work as normal with your current operating system. We strongly encourage you not to install iOS 4.2 until Apple fixes the upgrade issue. We will send out an email update as soon as it is safe to upgrade.

Sincerely,
The Toktumi/Line2 Team
So it is expected that Apple has handled this bug in the newly released iOS 4.2.1 GM build for developers , you can check out details in this post.