TV jokes about "800 free" and "clubbing"
Scene S3e22
Phoebe: Yeah, I know. Oh, good thing it's one of those 801 numbers. Right?
Ross: Phoebe, 800 is toll free, 801 is-is Utah.
Phoebe: No, no, no, oh no-no-no, 【it's has to be 800. (picks up the instruction manual to check the phone number) 'Cause all those big companies have 800 numbers, every one. (Finds the number) Yeah, every big Utah-based company has one.】
Rachel: Phoe-be!!
Phoebe: Sorry, I'm so sorry, I will pay you back.
.......
SCENE s3e23
Rachel: (entering) Hi! Okay, don't be mad at me, but I couldn't resist.
Monica: Brides magazines?
Rachel: Yes, and I know that you'd say no if he asked you, but I'm sorry; how great would you look walking down the aisle in this Donna Carin. (shows her the picture.)
Phoebe: (gasps) Oh, you so would! Oh, you should get that anyway. (They both look at her.)【 Like for clubbing.】
Monica: It is so weird, I know what I said, but uh, this morning, I was lying in bed I was, I was imagining what it would be like to say yes.

questions below

Question

TV jokes about "800 free" and "clubbing"
Scene S3e22
Phoebe: Yeah, I know. Oh, good thing it's one of those 801 numbers. Right?
Ross: Phoebe, 800 is toll free, 801 is-is Utah.
Phoebe: No, no, no, oh no-no-no, 【it's has to be 800. (picks up the instruction manual to check the phone number) 'Cause all those big companies have 800 numbers, every one. (Finds the number) Yeah, every big Utah-based company has one.】
Rachel: Phoe-be!!
Phoebe: Sorry, I'm so sorry, I will pay you back.
.......
SCENE s3e23
Rachel: (entering) Hi! Okay, don't be mad at me, but I couldn't resist.
Monica: Brides magazines?
Rachel: Yes, and I know that you'd say no if he asked you, but I'm sorry; how great would you look walking down the aisle in this Donna Carin. (shows her the picture.) 
Phoebe: (gasps) Oh, you so would! Oh, you should get that anyway. (They both look at her.)【 Like for clubbing.】 
Monica: It is so weird, I know what I said, but uh, this morning, I was lying in bed I was, I was imagining what it would be like to say yes.

questions below

Answer

Q1 - I assume she made a call to an 801 number, and thought that it was free, but got a big charge? 
I don't know why she said it has to be. Perhaps to explain why she rang it? Sorry - that kind of inane humour doesn't really mean much to me.
Q2 - yes, clubbing is going to a nightclub.

Answer

800 is a toll free number. 801 is an area code. If I remember the episode, it is the code for Utah. Phoebe is in New York. So, she thought the call was free but was really expensive.

To go to a nightclub.

Answer

Q1: Phoebe dialed the wrong number, she thought 801 was free, so she dialed 801. but everybody told her that 800 was free and she should have dialed 800. but why did phoebe say “it has to be 800”? i think it should be “it has to 801” because she thought 801 was free!

Q2: what is clubbing？ Going to club??