Fast-forward to a few weeks ago when I apply for a sysadmin position at a local ISP. Less than three weeks from applying, I am hired before the background check even clears. I started last Wednesday.
Today, I get an email from the first company saying they want to set up a phone interview.
I really don't know how to handle this. Do I play hardball and tell them I was already hired? Do I ask if they can beat the pay and benefits of my current position? Do I say I am still interested but have been employed elsewhere? Do I tell my current boss that I might be considering a better position at another company?
If pentesting is what you'd rather be doing, be up front with them about the situation. If you'd be willing to leave for a similar/better/wildly better offer, say so.
Do I tell my current boss that I might be considering a better position at another company?
No. Do not tell your current boss that you might be considering a better position at another company. If the company that you're not working for right now makes you an offer that you'd like to take, make 100% certain that you have a position there, and then notify your current employer that you're leaving. Under no circumstances should you indicate to them that you're thinking about leaving.
I wanna display interest without making it obvious that I am gonna push for the best offer from both parties.
Do not push for the best offer from both parties. The only communication you should have with your current employer about this situation is to notify them that you're leaving once you have employment elsewhere secured.
My advice might be different if you'd been working at your current place of employment for longer, and had reason to believe that they'd be willing to negotiate to keep you around. For an entry-level position (I'm assuming, based on the given context) that you've only been at for a few months, I wouldn't think that would be the case.
If being a pentester is what you want to do then take the interview, and if you decide to take the job then just quit from your current employer and tell them that the role wasn't what you were looking for.
Seriously, a decision that will potentially effect your career for the rest of your life shouldn't be done on the basis of etiquette, it should be done on the basis of what you want to do with your life.
Second a phone interview IS NOT a job offer. I am a 4.0 GPA double major undergrad and 3.9 GPA masters student with great recommendations and tons of individual side projects and part time school-related job experience, but no full time job experience. So far I've been accepted one place, I turned it down due to a condition that would mean I could not work until half a year passed. I have had over a dozen interviews and half a dozen phone interviews. Most places go resume -> phone interview -> company interview -> final steps, so that indicates you have passed 1/3 or 1/4 of the hurdles. Due to my skills nearly every resume turned in becomes a phone interview, the phone interviews pretty much always result in an interview, but most interviews dead-end because they find "another candidate with more experience." If your situation is anywhere near similar to mine, then you would have 50% chance at best of getting the pentester job, possibly closer to 10%.
My advice would be to take the sysadmin position and leave the soonest you feel comfortable (from what I've heard you should be there a year, at least half a year, any less than that looks really bad). If you look for a job and have even a single year of job experience, that should work in your favor. You have already accepted it AND you do not have another offer.
Do not try to game the system, simply tell them you accepted another offer already but would like to consider them the next time you are looking for a job. If you say, "Well I was just hired by someone else so you better make me a really good offer to make me turn traitor to my current company and leave them," that reflects horribly on your character and they will run. If you tell your current boss, "Hey I know you hired me last Wednesday, but I'm thinking of leaving" that will also reflect horribly on your character and could damage future opportunities (You do know the next company you apply for could ask your current boss what he thinks of you right?).
My advice is just to forget about the other offer and pretend it never happened, stay with your job at least half a year, and at that point if you hate your job, maybe start looking around again and ask that company if you could interview with them.
I would say that it would not hurt to take the phone interview. This doesn't mean you are going to leave your current position. The company could end the process at that point and solve the issue for you. If this is the case, at the very least you gain some more exposure to interviews. If you do get past the phone interview stage and progress to an offer you will have to make the hard decision then. If you did proceed with the phone interview I would take Bigiain's advice and be honest with them. As others have suggested, playing the two companies off each other would not be a good plan since you have already taken the job.
No, you're right. They could have at least acknowledged my existence =\
