The 26-year-old made his first start since September 2008 when Edinburgh travelled to Glasgow last weekend.
Callam had previously spent 15 months on the sidelines following hip surgery as a result of an injury picked up on the opening day of last season.
The Scotland international played 60 minutes at Firhill and has since told supporters that there is plenty more to come.
"Game-time will help me to get back into the swing of things," said Callam, who missed 24 Magners League games in a row before coming on as a replacement against the Scarlets at the beginning of this month.
"I have worked a lot on my strength and conditioning over the last year. But I still feel there are things I can work on and improve on.
"I was out for a long time, so the more you play the more confident you become.
"You start to get more familiar with all the systems. So I feel physically ready, but I feel that I need to improve upon my speed and agility and that will come with more game-time."
But while Callam was delighted to finally be back in the thick of things, he admits that the result that accompanied his return to the starting line up was hugely disappointing.
Edinburgh arrived in Glasgow joint top of the Magners League standings but defeat saw them slip out of the play off places and down into fifth spot.
Fortunately for Edinburgh, they have an immediate opportunity to make amends when they welcome Glasgow to Murrayfield on January 2. It's an opportunity Callam insists he and his team-mates are determined to grab with both hands.
"There is going to be a huge response this week," added Callam.
"We knew what we had to do, but we just didn't do it - that is the most disappointing thing. We need to get things right; especially on our home patch.
"The last few years we have been at home first, so this time around there is a change of scenery. They are coming to our house and we need to make sure we are fired up from the first kick off.
"In the first half, we hardly had any ball and there were a lot of uncharacteristic mistakes. There were guys getting turned over and lots of mistakes. We've got a bigger pitch to play on at the weekend and hopefully we can play a bit more rugby.
"It was a huge disappointment because of the way we performed and we will be doing everything we can to put it right on Saturday."
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