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The legality of it doesn't really matter. I don't mean to be rude but the OP has absolutely no idea what he is doing. For that reason alone he shouldn't be using beta software.
 
If he's willing to accept the possibility of nuking his phone without any support, what's it matter. If he's not willing, then I'd agree he shouldn't use it.
 
Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_10 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8E600 Safari/6533.18.5)

I had beta 4 iTunes until about 20 minutes ago, but my iTunes had been giving me that message since 122 hours before it was set to expire. Your only problem appears to be that your iTunes is still beta 4. Hence 10.5b48 or whatever, that is beta 4. Your phone should be fine, if it isn't, go back to 4.3.5 anytime.
 
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