Twitter on mobile phones only with Telstra?

[gd253]

I signed up to Twitter this weekend and for one site I wanted to have tweets sent to my phone via SMS (Thanks Dr Ron!). I was able to arrange this but the only carrier available was Telstra. No Optus (which I would've preferred), 3 or any others. Is this the usual state of affairs with Twitter?

I was lucky I had an old Telstra prepaid phone that I was able to set up.

--gd