I got the United Club Card and was also interested in travelling a couple days later. I called United and they did something and said I could just give my MP number and I should be fine. As it turns out, the card arrived two days after approval so I had it with me for travel.
LH lounge in BOS - the guy at the desk told me it was no good. I told him it was. He let me in. Thinking about this later, maybe he just gave in.
LH lounge in FRA - also told me I couldn't get in. I really needed to charge my phone so I pressed the issue. She was having none of it - see you later. So I called the support line and the guy who answered said Yes, I should be able to get in. He offered to talk to the woman at the door, but she would have none of it (theme). Eventually, he called someone in United in Germany and patched her in to our call. She said - why is this a question? United doesn't have any lounges in Germany, and the card is only good for United lounges.
Sigh. So I gave up and didn't try to get into the three other lounges on my trip. Re-reading the offer email I found this:
As the primary Cardmember, enjoy all these valuable benefits and more.
A United ClubSM Membership. You'll receive your United Club Card within 6 weeks of receiving your MileagePlus Club Credit Card. Your United Club Membership provides you with access to all United Club locations and participating Star Alliance® affiliated lounges worldwide.1
TERMS AND CONDITIONS
1 UNITED CLUB MEMBERSHIP: The primary cardmember can access the United Club starting 2 weeks after their account open date by presenting their MileagePlus number and photo identification upon entry to the Club (excludes Star Alliance and affiliated lounges).
Sooooo, you can get into all participating lounges, but no one is participating. Normally I'm pretty good at catching doublespeak so I kicked myself for not reading the details.
I would suggest the original poster might run into the same problems I did.