Dialing and contact search lacking up iPhone

About 3 weeks ago my 3gs started to lock up during dialing or contact searches. It wouldnt respond to pad touches, then would suddenly unlock and enter every key I had touched. Contact searches were useless. Ive done complete restores. Ive made 2 trips to the genius bar...theyve even swapped out the phone. The new phone was fine UNTIL I restored from backup...now its locking up. Voice dialing is fine, and generally dialing from favorites is ok. Im running 4.2.1, but this started prior to that. Ive ntocied the screens staggering a bit between changes.
hp Windows 7