They've called 2 or 3 times today.  I say hello, and then they immediately hang up.  Probably trying to collect active numbers for telemarketers or something.

Same experience here. We have received one call a day for five days. The caller just hangs up. Today we marked the call for trace with Sasktel by hanging up and then picking up the phone and dialing *57. You don't have to sign up for this service if you are a Sasktel customer. After 4 traces (occurences) Sasktel will take care of it if you follow up with a complaint.

they phone all day long but hang up when you answer.

They call here for 'Mrs Peterson', thinking that my boyfriend and I are married, and I'm using his last name.
When I tell them he's not around they say 'I'll call back later'. Usually I get "A local charity" but they won't tell me which one, but today I got "Shelley" and she hung up almost before she could finish her name.
It's a Regina number, and I'm pretty sure it's a scam.

this is who is calling you.  don't ask me why.
Xentel Telemarketing
Regina, SK
2024 Albert Street, Unit A
Regina, SK,  S4P 2T7
Tel: (306) 347-7410
Fax: (306) 347-7419

They have limited staff and an autodialer - and so if no staff are available to answer when you pick up, the autodialer hangs up. And calls you later.