I happen to have a grandfathered Sprint SERO plan, so I'm not going anywhere.

However, if I was going to use Straight Talk or any of these other discount pre-pay services, I would first port my number to Google Voice. I would then have my Google Voice number forward to the prepaid phone, and I would make outgoing calls through GV as well so the GV number would show in caller ID.

Incoming and outgoing SMS would also be through Google Voice. Yes, it does not do outgoing international SMS nor MMS.

For traveling abroad, I would have GV forward to a US forwarding number that would forward to my foreign SIM.

Given the lack of customer service on these prepaid services, keeping the number with GV would be an added layer of protection if something went wrong with the prepaid account. Also, I like the GV voicemail.