The 28-year-old Hurricanes back rower signed a three-year contract with the club back in February, and says he's has been following the Warriors progress ever since.
Talking to glasgowwarriors.org, Callum said: "It's been a long time coming, to be honest.
"It's probably getting close to eight months since we agreed the deal, so it's nice to finally touch down and get here. Once I knew I was coming, I kept an eye on the team and the guys to see how they were doing."
The New Plymouth native recently completed his first day of training with his new side, and is grateful for the welcome from his new team-mates.
"It's amazing - I just turned up and there's a house full of food and a list of things I can do around the city!" said Callum.
"The guys have been great, so accommodating. I've only been here for a few days but it feels like I've been here for much longer already."
Callum is under no illusion as to the level of competition for places in the Glasgow back row.
"The group look like they're going really well, so it'll be highly contested for sure."
Callum made 15 appearances for the Hurricanes in their impressive run to the Super Rugby semi-finals as well as being named as Team Man of the Year at the end-of-season awards dinner.
"It was a great season, and it's always been my dream to play for the 'Canes' said Callum.
"I suppose, in the end, it was a little disappointing - we had a pretty similar team to the one that won Super Rugby a year before, so to lose the semi-final in Johannesburg was a bit of a downer. I'm looking forward to something new though, and that's what Glasgow are providing me with."
Despite having a long 2017 season behind him, Callum says he's keen to get going at Scotstoun, under the watchful eye of two men that he knows well.
He said: “It's been a long year in New Zealand, but I've had a couple of weeks off and I'm itching to get back out and do some training.
"It's pretty similar to what I'm used to - I know Rens [Dave Rennie] and Jason [O'Halloran], so from what I've seen so far it’s a pretty fast style of rugby, which I'm excited about. The boys are buying into it and it's going great.
"Jason was the academy manager back in Manawatu when I was 19 or 20, and I worked with him right up until he left for Scotland. I was lucky enough to play under him when Manawatu won its first ever championship (in 2014), which was pretty special. Rens brought me through for Manawatu in 2009 and we've come up against each other in Super Rugby. It's good to be working with them both again."
So what kind of player can the Scotstoun crowd expect to see in action?
"Not a very fast one!" laughed Callum.
"I just think my way around things and use my head a bit more now that I'm getting a bit older. I like to think I'm a hard worker and let my actions do the talking.
"I sat down the other night and had a think about what I want to achieve. I'm not too sure what the coaches have got planned for me, but I want to prove that I'm here to play rugby, not to muck around. I don't think I've played my best rugby yet, so I'm looking forward to pushing on here."