Why does calling my wife's phone go straight to VoiceMail?
It could be your number being "blacklisted" on your wife's phone. There are a lot of apps on the playstore offering this feature, and some Android versions can do so on their own (just configure the contact in your contacts list correspondingly).

So here's what you could do:


check with your SIM card placed in some other phone (if that option exists; at least here in Europe we can move the SIM card around). Your call should be still blocked/routed to voicemail then, so you know the issue is not with your phone (e.g. dialing some prefix/postfix)
check your wife's phone for installed apps like Advanced Call Blocker etc.
check your wife's phonebook (errm, or let her check ;) for your record there and see whether it is blacklisted. If unsure, just delete it temporarily, then call her again.
At least CyanogenMod lets you manage a separate blacklist. With CM, it is found in the call settings. Check whether your number made it into this place.
if the problem still exists, repeat step 1. with your wife's phone (again, if possible)


My guess is either 2., 3., or 4. will reveal the cause.