Foster has made the £6million switch to St Andrew's after missing out on Fabio Capello's squad for the World Cup finals this summer.
He had effectively become third choice at Manchester United - behind Edwin van der Sar and Tomasz Kuszczak.
On a mission: Keeper Foster is desperate to be involved with England again
But the 27-year-old is looking to make the same impact for Birmingham as Joe Hart, who is heading to South Africa with England after a successful season on loan from Manchester City.
Foster said: 'I know I was at Manchester United, the biggest club in the world, but I don't enjoy not playing regular first-team football.
'Training is all well and good but matches do it for me. In the last two or three years I've played 20-odd games and it is no good and to be fair to Edwin, he can go on for another two or three years.
'He is that fit. I think the main concern was, when Edwin signed his new deal, everyone knew he is going to be the No 1 keeper next season.
'He could go on for another few years after that as well. He is a fantastic keeper. I'm 27, I just need first-team football now, enough is enough and it is time to move on.'
Foster admitted: 'The lack of football has cost me at the end of the day in terms of England.
'I am not on the plane to South Africa and I can't argue with the manager's decision. I've played one (first-team) game in seven months.
'I've seen Mr Capello at a few matches with United this season and he has asked me what is going on and things like that.
Fresh start: Foster will be playing for Birmingham boss Alex McLeish next season
'I think he will be fairly pleased that I am looking to play some first-team football now.
'I'll get behind the country now like the rest of the fans and hope we do really well in the tournament.
'For me the aim is to well with Birmingham and get back with England for the next European Championships.'
Foster is adamant his relationship with Sir Alex Ferguson remains undamaged after bringing to an end his five-year spell at United.
He said: 'Had my relationship with Sir Alex become strained by the end? No definitely not. I've read quite a few things saying that we had a massive barney after the Sunderland game.
'A barney involves two people talking. It was mainly just one person. But the relationship was definitely not strained.
'Sir Alex has been fantastic with me and I've read some nice things he said the other day which is fantastic to hear.
'It gives you a boost. You never have to say anything when a player leaves his club. I got on with the manager really well up until the end which unfortunately had to come.'
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