I reverted from 5.0 to 2.8 because 5.0's DTMF implementation is horribly fucking broken and shitty. It fails consistently if somewhat randomly (that is, I can't predict _when_ in a call it will be broken, but I can predict that it _will_ be broken), and they fall back on some sort of dopey standards excuse. Alls I knows is, before the upgrade DTMF worked with any voicemail/conferencing/phonetree system I dialed with 2.8 but failed almost always at some point using 5.0. They need to digitize a PCM sample of all DTMF tones around the world and produce them for as long as you press the number key, with the appropriate tone for the appropriate country (if there's any local variations) given the phone #.
Also, while 2.8 would choke on phone #s without leading country codes (it would say that my unlimited US/Canada plan was not eligible to dial a 10-digit US number, retardation) and 5.0 seemed to handle it better, the 5.0 interface is AWFUL, and it doesn't let you put phone #s in the 'contact' text entry bar, you have to call up the dialpad.