Ask HN: Switching my site's SMS capabilities over to Twitter. Good or bad idea?

Hi HN, I'd like your input on something. My site allows people to add information to their account via email and SMS, and it also sends out notifications to email/SMS. I had an idea to completely replace my homemade SMS functionality with twitter.

Notifications (outgoing): Using email gateways for SMS is unreliable and only available to a few carriers. With twitter, my users would just have to provide their twitter username. My app would then send out a DM and they would get a text message from twitter.

Incoming: A simple "d soshiku [query]" sent to 40404 and that's it. My app doesn't actually offer "true texting" since they have to send their text to an email address.

The problem is, there's a couple thousand people with their phone credentials hooked up to their accounts. I would essentially have to force them to sign up with twitter if they'd like to continue using the SMS services.

Do you think this a good idea, or a foolish one? Thanks.

Edit: My site is free, though I am working on paid plans.