Cydia > Search > SBRotator And download. Its a bit buggy, not as much anymore, but it gives your iPhone a popular iPad feature.
This is about rotating the lockscreen not about rotating the springboard. Its made by the same guy but apparently not out yet. SBrotator does not apply to the lockscreen. Again please know your stuff before you post...
Like I said. LSrotator is in beta and you can get the link for the beta repo if you follow limneos on Twitter
LSRotator has a bug where the accelerometer doesn't work in apps. I don't know if they fixed it yet, I tried it like 2 days ago.
Works GREAT ! It works just fine on my phone, Im running 3.1.3 btw. This is a mod that I have been waiting for
To completely landscape your phone. Think about lsrotator and sbrotator, landscape phone. then set things to open automatically to landscape if possible and bam!
Both are close but not quite there for me yet. I'm hoping Limneos finally gets all the bugs out and we can have our phones whichever way we want!!
Sorry, I have five rows and five columns installed and it doesn't quite work. Limneos reproduced my bugs and is working on it. Your results may vary and I'm glad it works for you!