Many CPI campaigns in mobpartner have this. many also without landing pages. How do you deal with this? Simply put their creatives or search other network for CPI offers?
I'm sure most just use their own anyway, at least to do a quick test.
you can ask your AM and show him your custom banners. Most of the time they will allow
Ask your AM. Usually it turns out that "no custom creatives" means "ask nicely first". 
MobPartner sucks for this.
If you can find an actual AM there though...
I first joined there years ago (haven't run anything with them really) and asked about custom creatives and if I could have an AM to approve them.
They just said 'no'. 'If a campaign says no custom creatives then you must comply'. Ok...
Similar story with Ad4Game. Tonnes of offers, care more about mindless pubs not media buyers. Volume changes everything but it doesn't stimulate much enthusiasm when they seem to have no rapport with media buyers.
Then what network with many CPIs for mobile is recommended ?
glispa
Zeno, what's your recommendation after mobpartner and ad4games?
Lots of networks are heading into the mobile space hard. I'd actually struggle to think of a network I'm with who don't have quite a lot of mobile offers at this point.