With Andrew Hore retired, and Corey Flynn heading to France, the ball appears to be in the court of either Coltman or Chiefs hooker Nathan Harris.
Hurricanes hooker Dane Coles, after putting on some weight over the off-season and impressing in recent weeks, appears to be the No 1 option, while veteran Keven Mealamu will be there if his creaking 35-year-old body holds together.
Coltman (24) and Harris (22) are both former New Zealand Colts hookers who trained with the All Blacks last season in an apprentice scheme.
But neither has been totally convincing in the Super 15 this season, and performances at the camps over the next couple of weeks may be vital for both players.
Coltman started strongly for the Highlanders this season but had a poor game against the Force. He has come back reasonably well without being totally compelling.
The physical education student has a big engine and is a sound scrummager. He has had issues with throwing the ball in - he started his rugby career as a prop, and only converted to hooker when he left school - but has improved over the past year.
But the Bay of Plenty rake was called into the Chiefs squad when Hika Elliot got injured, and with others in the Chiefs also going down with injury, Harris has taken his chance.
He gets round the field and can break the line but he, too, has had some difficulties finding his jumpers at lineout time.
Those throwing worries may have also hurt the chances of Crusaders hooker Ben Funnell.
The other three Highlanders to make the squad are predictable - Ben and Aaron Smith have had top years for the southern franchise, while Malakai Fekitoa was always going to be in the squad thanks to his form in the opening months of the season.
Other features of the squad include the naming of big Blues lock Patrick Tuipulotu, who played for the New Zealand under-20 side last year, and the reintroduction of Blues loose forward Jerome Kaino.
Kaino has impressed this year with his bruising style but it will be interesting whether he can keep up with the speed of the game played by the All Blacks in the past couple of seasons.
Victor Vito comes back into the frame after some good efforts for the Hurricanes while Colin Slade also enjoys a return.
Slade looks a different player from the hesitant and inaccurate No 10 who played for the Highlanders last year.
One wonders, though, whether he has done enough to get ahead of Beauden Barrett or Aaron Cruden.
Those unlucky to miss out include Crusaders back Tom Taylor, Hurricanes lock James Broadhurst and Hurricanes prop Jeffery Toomaga-Allen.
The camps are in Christchurch next week (May 18-20) and Wellington the week after (May 25-27).
Lock Jeremy Thrush is only available for the Wellington camp and Luke Whitelock will only attend the Christchurch camp.
The camp was limited to 35 players, and a 31-man squad for the tests against England will be named on June 1.
All Blacks
Wider training squad
Forwards: Keven Mealamu, Nathan Harris, Dane Coles, Liam Coltman, Charlie Faumuina, Tony Woodcock, Ben Franks,Wyatt Crockett, Owen Franks, Patrick Tuipulotu, Brodie Retallick, Jeremy Thrush, Dominic Bird, Sam Whitelock, Jerome Kaino, Steven Luatua, Sam Cane, Liam Messam, Victor Vito, Richie McCaw, Kieran Read, Luke Whitelock.
Backs: Tawera Kerr-Barlow, TJ Perenara, Aaron Smith, Aaron Cruden, Beauden Barrett, Colin Slade, Ma'a Nonu, Conrad Smith, Ryan Crotty, Malakai Fekitoa, Cory Jane, Julian Savea, Israel Dagg, Ben Smith.
